Working Draft 01, 10
June8 October 2003
Editors:
Francisco Curbera,
Yaron Goland, BEA <ygoland@bea.com>
Neelakantan Kartha,
Sterling Commerce <N_Kartha@stercomm.com>
Kevin Canyang Liu,
Prasad Yendluri,
webMethods <pyendluri@webmethods.com>
Contributors:
{FirstName} {Last Name}, {Organization}
This
document defines a notation for specifying business process behavior based on
Web Services. This notation is called Business Process Execution Language for
Web Services (abbreviated to BPEL4WS in the rest of this document). Processes
in BPEL4WS export and import functionality by using Web Service interfaces
exclusively.
Business
processes can be described in two ways. Executable business processes model actual
behavior of a participant in a business interaction. Business protocols, in
contrast, use process descriptions that specify the mutually visible message
exchange behavior of each of the parties involved in the protocol, without
revealing their internal behavior. The process descriptions for business
protocols are called abstract processes. BPEL4WS is meant to be used to model
the behavior of both executable and abstract processes.
BPEL4WS
provides a language for the formal specification of business processes and
business interaction protocols. By doing so, it extends the Web Services
interaction model and enables it to support business transactions. BPEL4WS
defines an interoperable integration model that should facilitate the expansion
of automated process integration in both the intra-corporate and the
business-to-business spaces.
This is
the very first draft version of the specification, converted to OASIS TC draft
format from the origninal BPEL4WS V1.1 specification dated
If you
are on the <wsbpel@lists.oasis-open.org> list for committee members, send comments
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"subscribe"as the body of the message.
For
information on whether any patents have been disclosed that may be essential to
implementing this specification, and any offers of patent licensing terms,
please refer to the Intellectual Property Rights section of the WS-BPEL TC web
page http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsbpel
Copyright © 2003
OASIS Open, Inc. All Rights Reserved.
Table of Contents
1. Introduction
4. What Changed from
BPEL4WS 1.0
4.1. Core Concepts Clarification
4.2. Terminology Changes
4.3. Feature Changes
5. Core Concepts and
Usage Patterns
6. Defining a Business
Process
6.1. Initial Example
6.2. The Structure of a Business Process
6.4. The Lifecycle of a Business Process
7. Partner Link
Types, Partner Links, and Endpoint References
7.1. Partner Link Types
7.2. Partner Links
7.3. Business Partners
7.4. Endpoint References
8.1. Motivation
8.2. Defining Properties
9.1. Expressions
9.2. Variables
9.3. Assignment
10. Correlation
10.1. Message Correlation
10.2. Defining and Using Correlation
Sets
11. Basic Activities
11.1. Standard Attributes for Each Activity
11.2. Standard Elements for Each Activity
11.3. Invoking Web Service Operations
11.4. Providing Web Service Operations
11.5. Updating Variable Contents
11.6. Signaling Faults
11.7. Waiting
11.8. Doing Nothing
12.1. Sequence
12.2. Switch
12.3. While
12.4. Pick
12.5. Flow
13. Scopes
13.1. Data Handling
13.2. Error Handling in Business Processes
13.3. Compensation Handlers
13.4. Fault Handlers
13.5. Event Handlers
13.6. Serializable Scopes
14. Extensions for
Executable Processes
14.1. Expressions
14.2. Variables
14.3. Assignment
14.4. Correlation
14.5. Web Service Operations
14.6. Terminating a Service Instance
14.7. Compensation
14.8. Event Handlers
15. Extensions for
Business Protocols
15.1. Variables
15.2. Assignment
16. Examples
16.1. Shipping Service
16.2. Loan Approval
16.3. Multiple Start Activities
Appendixes
D. XSD Schemas
E. Notices
The goal of the Web Services
effort is to achieve universal interoperability between applications by using
Web standards. Web Services use a loosely coupled integration model to allow
flexible integration of heterogeneous systems in a variety of domains including
business-to-consumer, business-to-business and enterprise application
integration. The following basic specifications originally defined the Web
Services space: SOAP, Web Services Description Language (WSDL), and Universal
Description, Discovery, and Integration (UDDI). SOAP defines an XML messaging
protocol for basic service interoperability. WSDL introduces a common grammar
for describing services. UDDI provides the infrastructure required to publish
and discover services in a systematic way. Together, these specifications allow
applications to find each other and interact following a loosely coupled,
platformindependent model.
Systems integration requires more
than the ability to conduct simple interactions by using standard protocols.
The full potential of Web Services as an integration platform will be achieved
only when applications and business processes are able to integrate their
complex interactions by using a standard process integration model. The
interaction model that is directly supported by WSDL is essentially a stateless
model of synchronous or uncorrelated asynchronous interactions. Models for
business interactions typically assume sequences of peer-to-peer message
exchanges, both synchronous and asynchronous, within stateful, long-running
interactions involving two or more parties. To define such business
interactions, a formal description of the message exchange protocols used by
business processes in their interactions is needed. The definition of such
business protocols involves precisely specifying the mutually visible message
exchange behavior of each of the parties involved in the protocol, without
revealing their internal implementation. There are two good reasons to separate
the public aspects of business process behavior from internal or private
aspects. One is that businesses obviously do not want to reveal all their
internal decision making and data management to their business partners. The
other is that, even where this is not the case, separating public from private
process provides the freedom to change private aspects of the process
implementation without affecting the public business protocol.
Business protocols must clearly
be described in a platform-independent manner and must capture all behavioral
aspects that have cross-enterprise business significance. Each participant can
then understand and plan for conformance to the business protocol without
engaging in the process of human agreement that adds so much to the difficulty
of establishing cross-enterprise automated business processes today.
What are the concepts required to
describe business protocols? And what is the relationship of these concepts to
those required to describe executable processes? To answer these questions,
consider the following::
·
Business
protocols invariably include data-dependent behavior. For example, a
supply-chain protocol depends on data such as the number of line items in an
order, the total value of an order, or a deliver-by deadline. Defining business
intent in these cases requires the use of conditional and time-out constructs.
·
The
ability to specify exceptional conditions and their consequences, including
recovery sequences, is at least as important for business protocols as the ability
to define the behavior in the "all goes well" case.
·
Long-running
interactions include multiple, often nested units of work, each with its own
data requirements. Business protocols frequently require cross-partner
coordination of the outcome (success or failure) of units of work at various
levels of granularity.
If we wish to provide precise
predictable descriptions of service behavior for crossenterprise business
protocols, we need a rich process description notation with many features
reminiscent of an executable language. The key distinction between public
message exchange protocols and executable internal processes is that internal
processes handle data in rich private ways that need not be described in public
protocols.
In thinking about the data
handling aspects of business protocols it is instructive to consider the
analogy with network communication protocols. Network protocols define the
shape and content of the protocol envelopes that flow on the wire, and the
protocol behavior they describe is driven solely by the data in these
envelopes. In other words, there is a clear physical separation between
protocol-relevant data and "payload" data. The separation is far less
clear cut in business protocols because the protocol-relevant data tends to be
embedded in other application data.
BPEL4WS uses a notion of message
properties to identify protocol-relevant data embedded in messages. Properties
can be viewed as "transparent" data relevant to public aspects as
opposed to the "opaque" data that internal/private functions use.
Transparent data affects the public business protocol in a direct way, whereas
opaque data is significant primarily to back-end systems and affects the
business protocol only by creating nondeterminism because the way it affects
decisions is opaque. We take it as a principle that any data that is used to
affect the behavior of a business protocol must be transparent and hence viewed
as a property.
The implicit effect of opaque
data manifests itself through nondeterminism in the behavior of services
involved in business protocols. Consider the example of a purchasing protocol.
The seller has a service that receives a purchase order and responds with
either acceptance or rejection based on a number of criteria, including
availability of the goods and the credit of the buyer. Obviously, the decision
processes are opaque, but the fact of the decision must be reflected as
behavior alternatives in the external business protocol. In other words, the
protocol requires something like a switch activity in the behavior of the
seller's service but the selection of the branch taken is nondeterministic.
Such nondeterminism can be modeled by allowing the assignment of a
nondeterministic or opaque value to a message property, typically from an enumerated
set of possibilities. The property can then be used in defining conditional
behavior that captures behavioral alternatives without revealing actual
decision processes. BPEL4WS explicitly allows the use of nondeterministic data
values to make it possible to capture the essence of public behavior while
hiding private aspects.
The basic concepts of BPEL4WS can
be applied in one of two ways. A BPEL4WS process can define a business protocol
role, using the notion of abstract process. For example, in a supply-chain
protocol, the buyer and the seller are two distinct roles, each with its own
abstract process. Their relationship is typically modeled as a partner link.
Abstract processes use all the concepts of BPEL4WS but approach data handling
in a way that reflects the level of abstraction required to describe public
aspects of the business protocol. Specifically, abstract processes handle only
protocol-relevant data. BPEL4WS provides a way to identify protocol-relevant
data as message properties. In addition, abstract processes use
nondeterministic data values to hide private aspects of behavior.
It is also possible to use
BPEL4WS to define an executable business process. The logic and state of the
process determine the nature and sequence of the Web Service interactions
conducted at each business partner, and thus the interaction protocols. While a
BPEL4WS process definition is not required to be complete from a private
implementation point of view, the language effectively defines a portable
execution format for business processes that rely exclusively on Web Service
resources and XML data. Moreover, such processes execute and interact with
their partners in a consistent way regardless of the supporting platform or
programming model used by the implementation of the hosting environment.
Even where private implementation
aspects use platform-dependent functionality, which is likely in many if not
most realistic cases, the continuity of the basic conceptual model between
abstract and executable processes in BPEL4WS makes it possible to export and
import the public aspects embodied in business protocols as process or role
templates while maintaining the intent and structure of the protocols. This is
arguably the most attractive prospect for the use of BPEL4WS from the viewpoint
of unlocking the potential of Web Services because it allows the development of
tools and other technologies that greatly increase the level of automation and
thereby lower the cost in establishing cross-enterprise automated business processes.
In summary, we believe that the
two usage patterns of business protocol description and executable business
process description require a common core of process description concepts. In
this specification we clearly separate the core concepts from the extensions
required specifically for the two usage patterns. The BPEL4WS specification is
focused on defining the common core, and adds only the essential extensions
required for each usage pattern.
BPEL4WS defines a model and a
grammar for describing the behavior of a business process based on interactions
between the process and its partners. The interaction with each partner occurs
through Web Service interfaces, and the structure of the relationship at the
interface level is encapsulated in what we call a partner link. The BPEL4WS
process defines how multiple service interactions with these partners are
coordinated to achieve a business goal, as well as the state and the logic
necessary for this coordination. BPEL4WS also introduces systematic mechanisms
for dealing with business exceptions and processing faults. Finally, BPEL4WS
introduces a mechanism to define how individual or composite activities within
a process are to be compensated in cases where exceptions occur or a partner
requests reversal.
BPEL4WS is layered on top of
several XML specifications: WSDL 1.1, XML Schema 1.0, and XPath1.0. WSDL
messages and XML Schema type definitions provide the data model used by BPEL4WS
processes. XPath provides support for data manipulation. All external resources
and partners are represented as WSDL services. BPEL4WS provides extensibility
to accommodate future versions of these standards, specifically the XPath and
related standards used in XML computation.
The keywords "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be
interpreted as described in [RFC 2119].
Namespace URIs of the general form
"some-URI" represent some application-dependent or context-dependent
URI as defined in [RFC 2396].
This specification uses an
informal syntax to describe the XML grammar of the XML fragments that follow:
·
The
syntax appears as an XML instance, but the values indicate the data types
instead of values.
·
Grammar
in bold has not been introduced earlier in the document, or is of particular
interest in an example.
·
<--
description --> is a placeholder for elements from some "other"
namespace (like ##other in XSD).
·
Characters
are appended to elements, attributes, and as follows: "?" (0 or 1),
"*" (0 or more), "+" (1 or more). The characters
"[" and "]" are used to indicate that contained items are
to be treated as a group with respect to the "?", "*", or
"+" characters.
·
Elements
and attributes separated by "|" and grouped by "(" and
")" are meant to be syntactic alternatives.
·
The
XML namespace prefixes (defined below) are used to indicate the namespace of
the element being defined.
·
Examples
starting with <?xml contain enough information to conform to this
specification; other examples are fragments and require additional information
to be specified in order to conform.
·
XSD
schemas and WSDL definitions are provided as a formal definition of grammars [XML Schema Part 1] and [WSDL 1.1].
BPEL4WS depends on the following
XML-based specifications: WSDL 1.1, XML Schema 1.0, XPath 1.0 and WS-Addressing.
Among these, WSDL has the most
influence on the BPEL4WS language. The BPEL4WS process model is layered on top
of the service model defined by WSDL 1.1. At the core of the BPEL4WS process
model is the notion of peer-to-peer interaction between services described in
WSDL; both the process and its partners are modeled as WSDL services. A
business process defines how to coordinate the interactions between a process
instance and its partners. In this sense, a BPEL4WS process definition provides
and/or uses one or more WSDL services, and provides the description of the
behavior and interactions of a process instance relative to its partners and
resources through Web Service interfaces. That is, BPEL4WS defines the message
exchange protocols followed by the business process of a specific role in the
interaction.
The definition of a BPEL4WS
business process also follows the WSDL model of separation between the abstract
message contents used by the business process and deployment information
(messages and portType versus binding and address information). In particular,
a BPEL4WS process represents all partners and interactions with these partners
in terms of abstract WSDL interfaces (portTypes and operations); no references
are made to the actual services used by a process instance.
However, the abstract part of
WSDL does not define the constraints imposed on the communication patterns
supported by the concrete bindings. Therefore a BPEL4WS process may define
behavior relative to a partner service that is not supported by all possible
bindings, and it may happen that some bindings are invalid for a BPEL4WS
process definition.
A BPEL4WS process is a reusable
definition that can be deployed in different ways and in different scenarios,
while maintaining a uniform application-level behavior across all of them. Note
that the description of the deployment of a BPEL4WS process is out of scope for
this specification.
The dependency on [WS-Addressing] is meant to
avoid inventing a private BPEL4WS mechanism for web service endpoint
references—such references are obviously a very general requirement in
the usage of web services.
The BPEL4WS 1.1 specification is
an enhancement of the BPEL4WS 1.0 specification [15]. The 1.1 version has five
new authors who brought a fresh viewpoint and deep industry experience. Their
contributions are reflected in a number of enhancements in this version.
The 1.1 version incorporates
numerous corrections and clarifications based on the feedback received on the
1.0 version. In addition, the 1.1 version differs from the 1.0 version in the
following substantive ways.
We believe that the two usage
patterns of business protocol description and executable business process
description require a common core of process description concepts. In the 1.1
version of the specification we clearly separate the core concepts from the
extensions required specifically for the two usage patterns. The main body of
the specification defines the core concepts. The Extensions for Executable
Processes and the Extensions for Business Protocols are defined in separate
sections at the end of the specification. The separation of core concepts from
extensions allows features required for specific usage patterns to be defined
in a composable manner. It is conceivable that further extensions will be
developed over time as the usage of the specification matures.
The following terminology changes
have occurred
·
Service
Links are now called Partner Links
·
Service
Link Types are now called Partner Link Types
·
Service
References are now called Endpoint References
·
Containers
are now called Variables
The formal syntax has also been
changed to reflect these terminology changes, including the replacement of the
current partner element with a partnerLink element to reflect
the fact that such a link is a conversational interface rather than reflective
of a business relationship. A partner element reflective of a business
relationship is added as described in the next section.
The following changes have been
made:
·
The terminate
activity is now strictly limited to executable processes.
·
Partner
Link Type Roles are now limited to a single WSDL portType.
·
A new
partner element is added to allow grouping of Partner Links based on
expected business enterprise relationships.
·
Endpoint
references (formerly service references) are now defined as given in [WS-Addressing]
·
Message
Properties are now limited to only be simple types.
·
Web
service interactions in abstract processes are now permitted to omit references
to variables for inbound and outbound message data.
·
Opaque
assignment in abstract processes may now target Boolean variables, and
variables of simple but unbounded types. In the latter case the semantics
requires creation of a unique value similar to a GUID.
·
The
syntax for defining variables has been changed to use three mutually exclusive
attributes messagetype, type and element. The first points to a WSDL message
type definition. The second points to an XML Schema simple type. The third
points to an XML Schema global element definition. This allows one to define
variables using something other than WSDL message types. Only variables that
are defined using messagetypes can be used as input or output targets in
messaging operations.
·
The
ability to provide an in-line WSDL message type has been removed, since the
vast majority of the uses of this feature will be replaced by the usage of XML
Schema simple types and global elements.
·
Correlation
sets have now been added to the uniqueness requirement so that it is not legal
to have two web service interactions outstanding if they have the same partner,
port type, operation and correlation set(s).
·
In
case of activity termination, the activities wait, reply and invoke
are added to receive as being instantly terminated rather than being
allowed to finish.
·
The
variable provided as the value of the faultVariable attribute in a catch
handler to hold fault data is now scoped to the fault handler itself
rather than being inherited from the associated scope.
·
Variables
and correlation sets can now be associated with local scopes rather than with
the process as a whole. This permits easier management of visibility and
lifetime for variables and repeated initiation of local correlation sets to
allow multiple correlated conversations during, e.g., iterative behavior.
·
Event
handlers can now be associated with scopes, to permit a process or scope to be
prepared to receive external events and requests concurrently with the main
activity of the process or scope. This is especially helpful for events and
requests that cannot be “scheduled” relative to the main activity,
but may occur at unpredictable times.
·
The
Future Directions section has been dropped since this version forms the
starting point for a formal standards process, which will define those
directions.
As noted in the introduction, we
believe that the two usage patterns of business protocol description and
executable business process description require a common core of process
description concepts. In this specification we clearly separate the core
concepts from the extensions required specifically for the two usage patterns.
The BPEL4WS specification is focused on defining the common core, and adds only
the essential extensions required for each usage pattern. These extensions are
described in separate sections (Extensions for Executable Processes
and Extensions for Business Protocols).
In a number of cases, the
behavior of a process in a certain combination of circumstances is undefined,
e.g., when a variable is used before being initialized. In the definition of
the core concepts we simply note that the semantics in such cases is not
defined.
BPEL4WS takes it as a general
principle that compliant implementations MAY choose to perform static analysis
to detect and reject process definitions that may have undefined semantics.
Such analysis is necessarily pessimistic and therefore might in some cases
prevent the use of processes that would not, in fact, create situations with
undefined semantics, either in specific uses or in any use.
In the executable usage pattern
for BPEL4WS, situations of undefined semantics always result in standard faults
in the BPEL4WS namespace. These cases will be described as part of the Extensions for Executable Processes in the
specification. However, it is important to note that BPEL4WS uses two standard internal
faults for its core control semantics, namely, bpws:forcedTermination and
bpws:joinFailure. These are the only two standard faults that play a role in
the core concepts of BPEL4WS. Of course, the occurrence of faults specified in
WSDL portType definitions during web service invocation is accounted for in the
core concepts as well.
Before describing the structure
of business processes in detail, this section presents a simple example of a
BPEL4WS process for handling a purchase order. The aim is to introduce the most
basic structures and some of the fundamental concepts of the language.
The operation of the process is
very simple, and is represented in the following figure. Dotted lines represent
sequencing. Free grouping of sequences represents concurrent sequences. Solid
arrows represent control links used for synchronization across concurrent
activities. Note that this is not meant to be a definitive graphical notation
for BPEL4WS processes. It is used here informally as an aid to understanding.
On receiving the purchase order
from a customer, the process initiates three tasks concurrently: calculating
the final price for the order, selecting a shipper, and scheduling the
production and shipment for the order. While some of the processing can proceed
concurrently, there are control and data dependencies between the three tasks.
In particular, the shipping price is required to finalize the price
calculation, and the shipping date is required for the complete fulfillment
schedule. When the three tasks are completed, invoice processing can proceed
and the invoice is sent to the customer.
The WSDL portType offered by the
service to its customers (purchaseOrderPT) is shown in the following WSDL
document. Other WSDL definitions required by the business process are included
in the same WSDL document for simplicity; in particular, the portTypes for the
Web Services providing price calculation, shipping selection and scheduling, and
production scheduling functions are also defined there. Observe that there are
no bindings or service elements in the WSDL document. A BPEL4WS process is
defined "in the abstract" by referencing only the portTypes of the
services involved in the process, and not their possible deployments. Defining
business processes in this way allows the reuse of business process definitions
over multiple deployments of compatible services.
The partner link types included
at the bottom of the WSDL document represent the interaction between the
purchase order service and each of the parties with which it interacts (see Partner
Link Types, Partner Links, and Endpoint References). Partner link types
can be used to represent dependencies between services, regardless of whether a
BPEL4WS business process is defined for one or more of those services. Each
partner link type defines up to two "role" names, and lists the
portTypes that each role must support for the interaction to be carried out
successfully. In this example, two partner link types, "purchasingLT"
and "schedulingLT", list a single role because, in the corresponding
service interactions, one of the parties provides all the invoked operations:
The "purchasingLT" partner link represents the connection between the
process and the requesting customer, where only the purchase order service
needs to offers a service operation ("sendPurchaseOrder"); the
"schedulingLT" partner link represents the interaction between the
purchase order service and the scheduling service, in which only operations of
the latter are invoked. The two other partner link types,
"invoicingLT" and "shippingLT", define two roles because
both the user of the invoice calculation and the user of the shipping service
(the invoice or the shipping schedule) must provide callback operations to
enable asynchronous notifications to be asynchronously sent
("invoiceCallbackPT" and "shippingCallbackPT" portTypes).
1234567890123456789012345678901234567890123456789012345678901234567890
1 2 3 4 5 6
<definitions targetNamespace="http://manufacturing.org/wsdl/purchase"
xmlns:sns="http://manufacturing.org/xsd/purchase"
xmlns:pos="http://manufacturing.org/wsdl/purchase"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://schemas.xmlsoap.org/wsdl/"
xmlns:plnk="http://schemas.xmlsoap.org/ws/2003/05/partner-link/">
<import namespace="http://manufacturing.org/xsd/purchase"
location="http://manufacturing.org/xsd/purchase.xsd"/>
<message name="POMessage">
<part name="customerInfo" type="sns:customerInfo"/>
<part name="purchaseOrder" type="sns:purchaseOrder"/>
</message>
<message name="InvMessage">
<part name="IVC" type="sns:Invoice"/>
</message>
<message name="orderFaultType">
<part name="problemInfo" type="xsd:string"/>
</message>
<message name="shippingRequestMessage">
<part name="customerInfo" type="sns:customerInfo"/>
</message>
<message name="shippingInfoMessage">
<part name="shippingInfo" type="sns:shippingInfo"/>
</message>
<message name="scheduleMessage">
<part name="schedule" type="sns:scheduleInfo"/>
</message>
<!-- portTypes supported by the purchase order process -->
<portType name="purchaseOrderPT">
<operation name="sendPurchaseOrder">
<input message="pos:POMessage"/>
<output message="pos:InvMessage"/>
<fault name="cannotCompleteOrder"
message="pos:orderFaultType"/>
</operation>
</portType>
<portType name="invoiceCallbackPT">
<operation name="sendInvoice">
<input message="pos:InvMessage"/>
</operation>
</portType>
<portType name="shippingCallbackPT">
<operation name="sendSchedule">
<input message="pos:scheduleMessage"/>
</operation>
</portType>
<!-- portType supported by the invoice services -->
<portType name="computePricePT">
<operation name="initiatePriceCalculation">
<input message="pos:POMessage"/>
</operation>
<operation name="sendShippingPrice">
<input message="pos:shippingInfoMessage"/>
</operation>
</portType>
<!-- portType supported by the shipping service -->
<portType name="shippingPT">
<operation name="requestShipping">
<input message="pos:shippingRequestMessage"/>
<output message="pos:shippingInfoMessage"/>
<fault name="cannotCompleteOrder"
message="pos:orderFaultType"/>
</operation>
</portType>
<!-- portType supported by the production scheduling process -->
<portType name="schedulingPT">
<operation name="requestProductionScheduling">
<input message="pos:POMessage"/>
</operation>
<operation name="sendShipingSchedule">
<input message="pos:scheduleMessage"/>
</operation>
</portType>
<plnk:partnerLinkType name="purchasingLT">
<plnk:role name="purchaseService">
<plnk:portType name="pos:purchaseOrderPT"/>
</plnk:role>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="invoicingLT">
<plnk:role name="invoiceService">
<plnk:portType name="pos:computePricePT"/>
</plnk:role>
<plnk:role name="invoiceRequester">
<plnk:portType name="pos:invoiceCallbackPT"/>
</plnk:role>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="shippingLT">
<plnk:role name="shippingService">
<plnk:portType name="pos:shippingPT"/>
</plnk:role>
<plnk:role name="shippingRequester">
<plnk:portType name="pos:shippingCallbackPT"/>
</plnk:role>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="schedulingLT">
<plnk:role name="schedulingService">
<plnk:portType name="pos:schedulingPT"/>
</plnk:role>
</plnk:partnerLinkType>
</definitions>
The business process for the
order service is defined next. There are four major sections in this process
definition:
·
The
<variables> section defines the data variables used by the process,
providing their definitions in terms of WSDL message types, XML Schema simple
types, or XML Schema elements. Variables allow processes to maintain state data
and process history based on messages exchanged.
·
The
<partnerLinks> section defines the different parties that interact with
the business process in the course of processing the order. The four
partnerLinks shown here correspond to the sender of the order (customer), as
well as the providers of price (invoicingProvider), shipment
(shippingProvider), and manufacturing scheduling services (schedulingProvider).
Each partner link is characterized by a partner link type and a role name. This
information identifies the functionality that must be provided by the business
process and by the partner service for the relationship to succeed, that is, the
portTypes that the purchase order process and the partner need to implement.
·
The
<faultHandlers> section contains fault handlers defining the activities
that must be performed in response to faults resulting from the invocation of
the assessment and approval services. In BPEL4WS, all faults, whether internal
or resulting from a service invocation, are identified by a qualified name. In
particular, each WSDL fault is identified in BPEL4WS by a qualified name formed
by the target namespace of the WSDL document in which the relevant portType and
fault are defined, and the ncname of the fault. It is important to note,
however, that because WSDL 1.1 does not require that fault names be unique
within the namespace where the operation is defined, all faults sharing a
common name and defined in the same namespace are indistinguishable. In spite
of this serious WSDL limitation, BPEL4WS provides a uniform naming model for
faults, in the expectation that future versions of WSDL will provide a better
fault-naming model.
·
The
rest of the process definition contains the description of the normal behavior
for handling a purchase request. The major elements of this description are
explained in the section following the process definition.
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<process name="purchaseOrderProcess"
targetNamespace="http://acme.com/ws-bp/purchase"
xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns:lns="http://manufacturing.org/wsdl/purchase">
<partnerLinks>
<partnerLink name="purchasing"
partnerLinkType="lns:purchasingLT"
myRole="purchaseService"/>
<partnerLink name="invoicing"
partnerLinkType="lns:invoicingLT"
myRole="invoiceRequester"
partnerRole="invoiceService"/>
<partnerLink name="shipping"
partnerLinkType="lns:shippingLT"
myRole="shippingRequester"
partnerRole="shippingService"/>
<partnerLink name="scheduling"
partnerLinkType="lns:schedulingLT"
partnerRole="schedulingService"/>
</partnerLinks>
<variables>
<variable name="PO" messageType="lns:POMessage"/>
<variable name="Invoice" messageType="lns:InvMessage"/>
<variable name="POFault" messageType="lns:orderFaultType"/>
<variable name="shippingRequest" messageType="lns:shippingRequestMessage"/>
<variable name="shippingInfo" messageType="lns:shippingInfoMessage"/>
<variable name="shippingSchedule" messageType="lns:scheduleMessage"/>
</variables>
<faultHandlers>
<catch faultName="lns:cannotCompleteOrder" faultVariable="POFault">
<reply partnerLink="purchasing"
portType="lns:purchaseOrderPT"
operation="sendPurchaseOrder"
variable="POFault"
faultName="cannotCompleteOrder"/>
</catch>
</faultHandlers>
<sequence>
<receive partnerLink="purchasing"
portType="lns:purchaseOrderPT"
operation="sendPurchaseOrder"
variable="PO">
</receive>
<flow>
<links>
<link name="ship-to-invoice"/>
<link name="ship-to-scheduling"/>
</links>
<sequence>
<assign>
<copy>
<from variable="PO" part="customerInfo"/>
<to variable="shippingRequest"
part="customerInfo"/>
</copy>
</assign>
<invoke partnerLink="shipping"
portType="lns:shippingPT"
operation="requestShipping"
inputVariable="shippingRequest"
outputVariable="shippingInfo">
<source linkName="ship-to-invoice"/>
</invoke>
<receive partnerLink="shipping"
portType="lns:shippingCallbackPT"
operation="sendSchedule"
variable="shippingSchedule">
<source linkName="ship-to-scheduling"/>
</receive>
</sequence>
<sequence>
<invoke partnerLink="invoicing"
portType="lns:computePricePT"
operation="initiatePriceCalculation"
inputVariable="PO">
</invoke>
<invoke partnerLink="invoicing"
portType="lns:computePricePT"
operation="sendShippingPrice"
inputVariable="shippingInfo">
<target linkName="ship-to-invoice"/>
</invoke>
<receive partnerLink="invoicing"
portType="lns:invoiceCallbackPT"
operation="sendInvoice"
variable="Invoice"/>
</sequence>
<sequence>
<invoke partnerLink="scheduling"
portType="lns:schedulingPT"
operation="requestProductionScheduling"
inputVariable="PO">
</invoke>
<invoke partnerLink="scheduling"
portType="lns:schedulingPT"
operation="sendShippingSchedule"
inputVariable="shippingSchedule">
<target linkName="ship-to-scheduling"/>
</invoke>
</sequence>
</flow>
<reply partnerLink="purchasing"
portType="lns:purchaseOrderPT"
operation="sendPurchaseOrder"
variable="Invoice"/>
</sequence>
</process>This section provides a quick
summary of the BPEL4WS syntax. It provides only a brief overview; the details
of each language construct are described in the rest of this document.
The basic structure of the
language is:
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<process name="ncname" targetNamespace="uri"
queryLanguage="anyURI"?
expressionLanguage="anyURI"?
suppressJoinFailure="yes|no"?
enableInstanceCompensation="yes|no"?
abstractProcess="yes|no"?
xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/">
<partnerLinks>?
<!-- Note: At least one role must be specified. -->
<partnerLink name="ncname" partnerLinkType="qname"
myRole="ncname"? partnerRole="ncname"?>+
</partnerLink>
</partnerLinks>
<partners>?
<partner name="ncname">+
<partnerLink name="ncname"/>+
</partner>
</partners>
<variables>?
<variable name="ncname" messageType="qname"?
type="qname"? element="qname"?/>+
</variables>
<correlationSets>?
<correlationSet name="ncname" properties="qname-list"/>+
</correlationSets>
<faultHandlers>?
<!-- Note: There must be at least one fault handler or default. -->
<catch faultName="qname"? faultVariable="ncname"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
</faultHandlers>
<compensationHandler>?
activity
</compensationHandler>
<eventHandlers>?
<!-- Note: There must be at least one onMessage or onAlarm handler. -->
<onMessage partnerLink="ncname" portType="qname"
operation="ncname" variable="ncname"?>
<correlations>?
<correlation set="ncname" initiate="yes|no"?>+
<correlations>
activity
</onMessage>
<onAlarm for="duration-expr"? until="deadline-expr"?>*
activity
</onAlarm>
</eventHandlers>
activity
</process>
The top-level attributes are as
follows:
·
queryLanguage.
This attribute specifies the XML query language used for selection of nodes in
assignment, property definition, and other uses. The default for this attribute
is XPath 1.0, represented by the URI of the XPath 1.0 specification: http://www.w3.org/TR/1999/REC-xpath-19991116.
·
expressionLanguage.
This attribute specifies the expression language used in the process. The
default for this attribute is XPath 1.0, represented by the URI of the XPath
1.0 specification: http://www.w3.org/TR/1999/REC-xpath-19991116.
·
suppressJoinFailure.
This attribute determines whether the joinFailure fault will be suppressed for
all activities in the process. The effect of the attribute at the process level
can be overridden by an activity using a different value for the attribute. The
default for this attribute is "no".
·
enableInstanceCompensation.
This attribute determines whether the process instance as a whole can be
compensated by platform-specific means. The default for this attribute is
"no".
·
abstractProcess.
This attribute specifies whether the process being defined is abstract (rather
than executable). The default for this attribute is "no".
The token "activity"
can be any of the following:
·
<receive>
·
<reply>
·
<invoke>
·
<assign>
·
<throw>
·
<terminate>
·
<wait>
·
<empty>
·
<sequence>
·
<switch>
·
<while>
·
<pick>
·
<flow>
·
<scope>
·
<compensate>
The syntax of each of these
elements, except <terminate>, is considered in the following paragraphs.
Although <terminate> is permitted as an interpretation of the token
activity, it is only available in executable processes and as such is defined
in the section on Extensions for Executable Processes .
The <receive> construct
allows the business process to do a blocking wait for a matching message to
arrive.
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<receive partnerLink="ncname" portType="qname" operation="ncname"
variable="ncname"? createInstance="yes|no"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?>+
</correlations>
</receive>
The <reply> construct
allows the business process to send a message in reply to a message that was
received through a <receive>. The combination of a <receive> and a
<reply> forms a request-response operation on the WSDL portType for the
process.
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<reply partnerLink="ncname" portType="qname" operation="ncname"
variable="ncname"? faultName="qname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?>+
</correlations>
</reply>
The <invoke> construct
allows the business process to invoke a one-way or requestresponse operation on
a portType offered by a partner.
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<invoke partnerLink="ncname" portType="qname" operation="ncname"
inputVariable="ncname"? outputVariable="ncname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?
pattern="in|out|out-in"/>+
</correlations>
<catch faultName="qname" faultVariable="ncname"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
<compensationHandler>?
activity
</compensationHandler>
</invoke>
The <assign> construct can
be used to update the values of variables with new data. An <assign>
construct can contain any number of elementary assignments. The syntax of the
assignment activity is:
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<assign standard-attributes>
standard-elements
<copy>+
from-spec
to-spec
</copy>
</assign>
The <throw> construct
generates a fault from inside the business process.
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<throw faultName="qname" faultVariable="ncname"? standard-attributes>
standard-elements
</throw>
The <wait> construct allows
you to wait for a given time period or until a certain time has passed. Exactly
one of the expiration criteria must be specified.
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<wait (for="duration-expr" | until="deadline-expr") standard-attributes>
standard-elements
</wait>
The <empty> construct
allows you to insert a "no-op" instruction into a business process.
This is useful for synchronization of concurrent activities, for instance.
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<empty standard-attributes>
standard-elements
</empty>
The <sequence> construct
allows you to define a collection of activities to be performed sequentially in
lexical order.
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<sequence standard-attributes>
standard-elements
activity+
</sequence>
The <switch> construct
allows you to select exactly one branch of activity from a set of choices.
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<switch standard-attributes>
standard-elements
<case condition="bool-expr">+
activity
</case>
<otherwise>?
activity
</otherwise>
</switch>
The <while> construct
allows you to indicate that an activity is to be repeated until a certain
success criteria has been met.
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<while condition="bool-expr" standard-attributes>
standard-elements
activity
</while>
The <pick> construct allows
you to block and wait for a suitable message to arrive or for a time-out alarm
to go off. When one of these triggers occurs, the associated activity is
performed and the pick completes.
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<pick createInstance="yes|no"? standard-attributes>
standard-elements
<onMessage partnerLink="ncname" portType="qname"
operation="ncname" variable="ncname"?>+
<correlations>?
<correlation set="ncname" initiate="yes|no"?>+
</correlations>
activity
</onMessage>
<onAlarm (for="duration-expr" | until="deadline-expr")>*
activity
</onAlarm>
</pick>
The <flow> construct allows
you to specify one or more activities to be performed concurrently. Links can
be used within concurrent activities to define arbitrary control structures.
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<flow standard-attributes>
standard-elements
<links>?
<link name="ncname">+
</links>
activity+
</flow>
The <scope> construct
allows you to define a nested activity with its own associated variables, fault
handlers, and compensation handler.
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<scope variableAccessSerializable="yes|no" standard-attributes>
standard-elements
<variables>?
... see above under <process> for syntax ...
</variables>
<correlationSets>?
... see above under <process> for syntax ...
</correlationSets>
<faultHandlers>?
... see above under <process> for syntax ...
</faultHandlers>
<compensationHandler>?
... see above under <process> for syntax ...
</compensationHandler>
<eventHandlers>?
...
</eventHandlers>
activity
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The <compensate> construct
is used to invoke compensation on an inner scope that has already completed
normally. This construct can be invoked only from within a fault handler or
another compensation handler.
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<compensate scope="ncname"? standard-attributes>
standard-elements
</compensate>
Note that the "standard-attributes"
referred to above are:
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name="ncname"?
joinCondition="bool-expr"?
suppressJoinFailure="yes|no"?
where the default values are as
follows:
·
name.
No default value (that is, unnamed)
·
joinCondition.
The logical OR of the liveness status of all links that are targeted at this
activity
·
suppressJoinFailure.
No
and that the "standard-elements"
referred to above are:
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<target linkName="ncname"/>*
<source linkName="ncname" transitionCondition="bool-expr"?/>*BPEL4WS contains constructs that
are generally sufficient for expressing abstract and executable business
processes. In some cases, however, it might be necessary to
“extend” the BPEL4WS language with additional constructs from other
XML namespaces.
BPEL4WS supports extensibility by
allowing namespace-qualified attributes to appear on any BPEL4WS element and by
allowing elements from other namespaces to appear within BPEL4WS defined
elements. This is allowed in the XML Schema specifications for BPEL4WS.
Extensions MUST NOT change the
semantics of any element or attribute from the BPEL4WS namespace.
As noted in the introduction, the
interaction model that is directly supported by WSDL is essentially a stateless
client-server model of synchronous or uncorrelated asynchronous interactions.
BPEL4WS, builds on WSDL by assuming that all external interactions of the
business process occur through Web Service operations. However, BPEL4WS
business processes represent stateful long-running interactions in which each
interaction has a beginning, defined behavior during its lifetime, and an end.
For example, in a supply chain, a seller's business process might offer a
service that begins an interaction by accepting a purchase order through an
input message, and then returns an acknowledgement to the buyer if the order
can be fulfilled. It might later send further messages to the buyer, such as
shipping notices and invoices. The seller's business process remembers the
state of each such purchase order interaction separately from other similar
interactions. This is necessary because a buyer might be carrying on many
simultaneous purchase processes with the same seller. In short, a BPEL4WS
business process definition can be thought of as a template for creating
business process instances.
The creation of a process
instance in BPEL4WS is always implicit; activities that receive messages (that
is, receive activities and pick activities) can be annotated to indicate that the
occurrence of that activity causes a new instance of the business process to be
created. This is done by setting the createInstance attribute of such an activity to "yes".
When a message is received by such an activity, an instance of the business
process is created if it does not already exist (see Providing Web Service Operations and Pick).
To be instantiated, each business
process must contain at least one such "start activity." This must be
an initial activity in the sense that there is no basic activity that logically
precedes it in the behavior of the process.
If more than one start activity
is enabled concurrently, then all such activities must use at least one
correlation set and must use the same correlation sets (see Correlation and the Multiple Start Activities example).
If exactly one start activity is
expected to instantiate the process, the use of correlation sets is
unconstrained. This includes a pick with multiple onMessage branches;
each such branch can use different correlation sets or no correlation sets.
A business process instance is
terminated in one of the following ways:
·
When
the activity that defines the behavior of the process as a whole completes. In
this case the termination is normal.
·
When
a fault reaches the process scope, and is either handled or not handled. In
this case the termination is considered abnormal even if the fault is handled
and the fault handler does not rethrow any fault. A compensation handler is
never installed for a scope that terminates abnormally.
·
When
a process instance is explicitly terminated by a terminate activity (see Terminating the Service Instance). In this case the termination is
abnormal.
·
If a
compensation handler is specified for the business process as a whole (see Compensation Handlers), a business process instance can be
compensated after normal completion by
platform-specific means. This functionality is enabled by setting the enableInstanceCompensation attribute of the process to "yes".
The structure of the main
processing section is defined by the outer <sequence> element, which
states that the three activities contained inside are performed in order. The
customer request is received (<receive> element), then processed (inside
a <flow> section that enables concurrent behavior), and a reply message
with the final approval status of the request is sent back to the customer
(<reply>). Note that the <receive> and <reply> elements are
matched respectively to the <input> and <output> messages of the
"sendPurchaseOrder" operation invoked by the customer, while the
activities performed by the process between these elements represent the
actions taken in response to the customer request, from the time the request is
received to the time the response is sent back (reply).
The example makes the implicit assumption
that the customer request can be processed in a reasonable amount of time,
justifying the requirement that the invoker wait for a synchronous response
(because this service is offered as a request-response operation). When that
assumption does not hold, the interaction with the customer is better modeled
as a pair of asynchronous message exchanges. In that case, the
"sendPurchaseOrder" operation is a one-way operation and the
asynchronous response is sent by invoking a second one-way operation on a
customer "callback" interface. In addition to changing the signature
of "sendPurchaseOrder" and defining a new portType to represent the
customer callback interface, two modifications need to be made in the preceding
example to support an asynchronous response to the customer. First, the partner
link type "purchasingLT" that represents the process-customer
connection needs to include a second role ("customer") listing the
customer callback portType. Second, the <reply> activity in the process
needs to be replaced by an <invoke> on the customer callback operation.
The processing taking place
inside the <flow> element consists of three <sequence> blocks
running concurrently. The synchronization dependencies between activities in
the three concurrent sequences are expressed by using "links" to
connect them. The links are defined inside the flow and are used to connect a
source activity to a target activity. (Note that each activity declares itself
as the source or target of a link by using the nested <source> and
<target> elements.) In the absence of links, the activities nested
directly inside a flow proceed concurrently. In the example, however, the
presence of two links introduces control dependencies between the activities
performed inside each sequence. For example, while the price calculation can be
started immediately after the request is received, shipping price can only be
added to the invoice after the shipper information has been obtained; this
dependency is represented by the link (named "ship-to-invoice") that
connects the first call on the shipping provider ("requestShipping")
with sending shipping information to the price calculation service
("sendShippingPrice"). Likewise, shipping scheduling information can
only be sent to the manufacturing scheduling service after it has been received
from the shipper service; thus the need for the second link
("ship-to-scheduling").
Observe that information is
passed between the different activities in an implicit way through the sharing
of globally visible data variables. In this example, the control dependencies
represented by links are related to corresponding data dependencies, in one
case on the availability of the shipper rates and in another on the
availability of a shipping schedule. The information is passed from the
activity that generates it to the activity that uses it by means of two global
data variables ("shippingInfo" and "shippingSchedule").
Certain operations can return
faults, as defined in their WSDL definitions. For simplicity, it is assumed
here that the two operations return the same fault
("cannotCompleteOrder"). When a fault occurs, normal processing is
terminated and control is transferred to the corresponding fault handler, as
defined in the <faultHandlers> section. In this example the handler uses
a <reply> element to return a fault to the customer (note the
"faultName" attribute in the <reply> element).
Finally, it is important to
observe how an assignment activity is used to transfer information between data
variables. The simple assignments shown in this example transfer a message part
from a source variable to a message part in a target variable, but more complex
forms of assignments are also possible.
A very important, if not the most
important, use case for BPEL4WS will be in describing cross-enterprise business
interactions in which the business processes of each enterprise interact
through Web Service interfaces with the processes of other enterprises. An
important requirement for realistic modeling of business processing in this
environment is the ability to model the required relationship with a partner
process. WSDL already describes the functionality of a service provided by a
partner, at both the abstract and concrete levels. The relationship of a
business process to a partner is typically peer-to-peer, requiring a two-way
dependency at the service level. In other words, a partner represents both a
consumer of a service provided by the business process and a provider of a
service to the business process. This is especially the case when the
interactions are based on asynchronous messaging rather than on remote
procedure calls. The notion of Partner links is used to directly model
peer-to-peer conversational partner relationships. Partner links define the
shape of a relationship with a partner by defining the message and port types
used in the interactions in both directions. However, the actual partner
service may be dynamically determined within the process. BPEL4WS uses a notion
of endpoint reference [WS-Addressing]
to represent the dynamic data required to describe a partner service endpoint.
It is important to emphasize that
the notions of partner link and endpoint reference used here are preliminary.
The specification for these concepts as they relate to Web Services is still
evolving, and we expect normative definitions for them to emerge in future. The
BPEL4WS specification will be updated to conform to the expected future standards.
A partner link type characterizes
the conversational relationship between two services by defining the
"roles" played by each of the services in the conversation and
specifying the portType provided by each service to receive messages within the
context of the conversation. The following example illustrates the basic syntax
of a partner link type declaration:
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<partnerLinkType name="BuyerSellerLink"
xmlns="http://schemas.xmlsoap.org/ws/2003/05/partner-link/">
<role name="Buyer">
<portType name="buy:BuyerPortType"/>
</role>
<role name="Seller">
<portType name="sell:SellerPortType"/>
</role>
</partnerLinkType>
Each role specifies exactly one
WSDL portType.
In the common case, portTypes of
the two roles originate from separate namespaces. However, in some cases, both
roles of a partner link type can be defined in terms of portTypes from the same
namespace. The latter situation occurs for partner link types that define
"callback" relationships between services.
The partner link type definition
can be a separate artifact independent of either service's WSDL document.
Alternatively, the partner link type definition can be placed within the WSDL
document defining the portTypes from which the different roles are defined.
The extensibility mechanism of
WSDL 1.1 is used to define partnerLinkType as a new definition type to be
placed as an immediate child element of a <wsdl:definitions> element in
all cases. This allows reuse of the WSDL target namespace specification and,
more importantly, its import mechanism to import portTypes. For cases where a
partnerLinkType declaration is linking the portTypes of two different services,
the partnerLinkType declaration can be placed in a separate WSDL document (with
its own targetNamespace).
The syntax for defining a
partnerLinkType is:
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<definitions name="ncname" targetNamespace="uri"
xmlns="http://schemas.xmlsoap.org/wsdl/"
xmlns:plnk="http://schemas.xmlsoap.org/ws/2003/05/partner-link/">
...
<plnk:partnerLinkType name="ncname">
<plnk:role name="ncname">
<plnk:portType name="qname"/>
</plnk:role>
<plnk:role name="ncname">?
<plnk:portType name="qname"/>
</plnk:role>
</plnk:partnerLinkType>
...
</definitions>
This defines a partner link type
in the namespace indicated by the value of the "targetNamespace"
attribute of the WSDL document element. The portTypes identified within roles
are referenced by using QNames as for all top-level WSDL definitions.
Note that in some cases it can be
meaningful to define a partner link type containing exactly one role instead of
two. That defines a partner linking scenario where one service expresses a
willingness to link with any other service, without placing any requirements on
the other service.
Examples of partnerLinkType
declarations are found in various business process examples in this
specification.
The services with which a
business process interacts are modeled as partner links in BPEL4WS. Each
partner link is characterized by a partnerLinkType. More than one partner link
can be characterized by the same partnerLinkType. For example, a certain
procurement process might use more than one vendor for its transactions, but
might use the same partnerLinkType for all vendors.
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<partnerLinks>
<partnerLink name="ncname" partnerLinkType="qname"
myRole="ncname"? partnerRole="ncname"?>+
</partnerLink>
</partnerLinks>
Each partnerLink is named, and
this name is used for all service interactions via that partnerLink. This is critical,
for example, in correlating responses to different partnerLinks for
simultaneous requests of the same kind (see Invoking Web
Service Operations and Providing Web Service Operations).
The role of the business process
itself is indicated by the attribute myRole and the role of the
partner is indicated by the attribute partnerRole. In the degenerate
case where a partnerLinkType has only one role, one of these attributes is
omitted as appropriate.
Note that the partnerLink
declarations specify the static shape of the relationships that the BPEL4WS
process will employ in its behavior. Before operations on a partner's service
can be invoked via a partnerLink, the binding and communication data for the
partner service must be available. The relevant information about a partner
service can be set as part of business process deployment. This is outside the
scope of BPEL4WS. However, it is also possible to select and assign actual
partner services dynamically, and BPEL4WS provides the mechanisms to do so via
assignment of endpoint references. In fact, because the partners are likely to
be stateful, the service endpoint information needs to be extended with
instance-specific information. BPEL4WS allows the endpoint references
implicitly present in partnerLinks to be both extracted and assigned
dynamically, and also to be set more than once. See Assignment
for the mechanisms used for dynamic assignment of endpoint references to
partner services.
While a partner link represents a
conversational relationship between two partner processes, relationships with a
business partner in general require more than a single conversational
relationship to be established. To represent the capabilities required from a
business partner, BPEL4WS uses the partner element. A partner is
defined as a subset of the partner links of the process, as shown in the
example below.
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<partner name="SellerShipper"
xmlns="http://schemas.xmlsoap.org/ws/2003/05/partner-link/">
<partnerLink name="Seller"/>
<partnerLink name="Shipper"/>
</partner>
Partner definitions are optional
and need not cover all the partner links defined in the process. From the
process perspective a partner definition introduces a constraint on the
functionality that a business partner is required to provide. In the example
above, the partner definition states that the same business partner (“SellerShipper”)
is required to provide the services associated with the the roles of seller and
shipper. Partner definitions MUST NOT overlap, that is, a partner link MUST NOT
appear in more than one partner definition.
The syntax for partner
definitions is given below:
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<partners>
<partner name="ncname">+
<partnerLink name="ncname"/>+
</partner>
</partners>WSDL makes an important
distinction between portTypes and ports. PortTypes define abstract
functionality by using abstract messages. Ports provide actual access
information, including communication endpoints and (by using extension elements)
other deploymentrelated information such as public keys for encryption.
Bindings provide the glue between the two. While the user of a service must be
statically dependent on the abstract interface defined by portTypes, some of
the information contained in port definitions can typically be discovered and
used dynamically.
The fundamental use of endpoint
references is to serve as the mechanism for dynamic communication of
port-specific data for services. An endpoint reference makes it possible in BPEL4WS
to dynamically select a provider for a particular type of service and to invoke
their operations. BPEL4WS provides a general mechanism for correlating messages
to stateful instances of a service, and therefore endpoint references that
carry instance-neutral port information are often sufficient. However, in
general it is necessary to carry additional instance-identification tokens in
the endpoint reference itself.
BPEL4WS uses the notion of
endpoint reference defined in [WS-Addressing].
Every partner role in a partnerLink in a BPEL4WS process instance is assigned a
unique endpoint reference in the course of the deployment of the process or
dynamically by an activity within the process.
The data in a message consists
conceptually of two parts: application data and protocolrelevant data, where
the protocols can be business protocols or infrastructure protocols providing
higher quality of service. An example of business protocol data is the
correlation tokens that are used in correlation sets (see Correlation).
Examples of infrastructure protocols are security, transaction, and reliable
messaging protocols. The business protocol data is usually found embedded in
the application-visible message parts, whereas the infrastructure protocols
almost always add implicit extra parts to the message types to
represent protocol headers that are separate from application data. Such
implicit parts are often called message context because they relate to
security context, transaction context, and other similar middleware context of
the interaction. Business processes might need to gain access to and manipulate
both kinds of protocol-relevant data. The notion of message properties is
defined as a general way of naming and representing distinguished data elements
within a message, whether in application-visible data or in message context.
For a full accounting of the service description aspects of infrastructure
protocols, it is necessary to define notions of service policies, endpoint
properties, and message context. This work is outside the scope of BPEL4WS.
Message properties are defined here in a sufficiently general way to cover
message context consisting of implicit parts, but the use in this specification
focuses on properties embedded in application-visible data that is used in the
definition of business protocols and abstract business processes.
A property definition creates a
globally unique name and associates it with an XML Schema simple type. The
intent is not to create a new type. The intent is to create a name that has
greater significance than the type itself. For example, a sequence number can
be an integer, but the integer type does not convey this significance, whereas
a globally named sequence-number property does. Properties can occur anywhere
in a message, including in the message context.
A typical use for a property in
BPEL4WS is to name a token for correlation of service instances with messages.
For example, a social security number might be used to identify an individual
taxpayer in a long-running multiparty business process regarding a tax matter.
A social security number can appear in many different message types, but in the
context of a tax-related process it has a specific significance as a taxpayer
ID. Therefore a global name is given to this use of the type by defining a
property, as in the following example:
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<definitions name="properties"
targetNamespace="http://example.com/properties.wsdl"
xmlns:tns="http://example.com/properties.wsdl"
xmlns:txtyp="http://example.com/taxTypes.xsd"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define a correlation property -->
<bpws:property name="taxpayerNumber"
type="txtyp:SSN"/>
...
</wsdl:definitions>
In correlation, the property name
must have global significance to be of any use. Properties such as price, risk,
response latency, and so on, which are used in conditional behavior in a
business process, have similar global and public significance. It is likely
that they will be mapped to multiple messages, and therefore they need to be
globally named as in the case of correlation properties. Such properties are
essential, especially in abstract processes.
The WSDL extensibility mechanism
is used to define properties so that the target namespace and other useful
aspects of WSDL are available.
The BPEL4WS standard namespace,
"http//schemas.xmlsoap.org/ws/2003/03/business-process/", is used for property definitions.
The syntax for a property definition is a new kind of WSDL definition as
follows:
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<wsdl:definitions name="ncname"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/">
<bpws:property name="ncname" type="qname"/>
...
</wsdl:definitions>
Properties used in business
protocols are typically embedded in application-visible message data. The
notion of aliasing is introduced to map a global property to a field in a
specific message part. The property name becomes an alias for the message part
and location, and can be used as such in Expressions
and Assignment in abstract business processes.
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<definitions name="properties"
targetNamespace="http://example.com/properties.wsdl"
xmlns:tns="http://example.com/properties.wsdl"
xmlns:txtyp="http://example.com/taxTypes.xsd"
xmlns:txmsg="http://example.com/taxMessages.wsdl"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define a correlation property -->
<bpws:property name="taxpayerNumber" type="txtype:SSN"/>
...
<bpws:propertyAlias propertyName="tns:taxpayerNumber"
messageType="txmsg:taxpayerInfo" part="identification"
query="/socialsecnumber"/>
</bpws:propertyAlias>
</definitions>
The bpws:propertyAlias defines a globally named property tns:taxpayerNumber as an alias for a location in the identification part of the message type txmsg:taxpayerInfo.
The syntax for a propertyAlias
definition is:
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<definitions name="ncname"
...
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/">
<bpws:propertyAlias propertyName="qname"
messageType="qname" part="ncname" query="queryString"/>
...
</wsdl:definitions>
The interpretation of the
message, part, and query attributes is the same as in the corresponding
from-spec in copy assignments (see Assignment).
Business processes model stateful
interactions. The state involved consists of messages received and sent as well
as other relevant data such as time-out values. The maintenance of the state of
a business process requires the use of state variables, which are called
variables in BPEL4WS. Furthermore, the data from the state needs to be
extracted and combined in interesting ways to control the behavior of the
process, which requires data expressions. Finally, state update requires a
notion of assignment. BPEL4WS provides these features for XML data types and
WSDL message types. The XML family of standards in these areas is still evolving,
and using the process-level attributes for query and expression languages
provides for the incorporation of future standards.
The extensions required for
abstract and executable processes are concentrated in the datahandling feature
set. Executable processes are permitted to use the full power of data selection
and assignment but are not permitted to use nondeterministic values. Abstract
processes are restricted to limited manipulation of values contained in message
properties but are permitted to use nondeterministic values to reflect the
consequences of hidden private behavior. Detailed differences are specified in
the following sections.
BPEL4WS uses several types of
expressions. The kinds of expressions used are as follows (relevant usage
contexts are listed in parentheses):
·
Boolean-valued
expressions (transition conditions, join conditions, while condition, and
switch cases)
·
Deadline-valued
expressions ("until" attribute of onAlarm and wait)
·
Duration-valued
expressions ("for" attribute of onAlarm and wait)
·
General
expressions (assignment)
BPEL4WS provides an extensible
mechanism for the language used in these expressions. The language is specified
by the expressionLanguage attribute of the process element. Compliant implementations of the
current version of BPEL4WS MUST support the use of XPath 1.0 as the expression
language. XPath 1.0 is indicated by the default value of the expressionLanguage attribute, which is:
http://www.w3.org/TR/1999/REC-xpath-19991116
Given an expression language, it
must be possible to query data from variables, to extract property values, and
to query the status of links from within expressions. This specification
defines those functions for XPath 1.0 only, and it is expected that other
expressionlanguage bindings will provide equivalent functionality. The rest of
this section is specific to XPath 1.0.
BPEL4WS introduces several
extension functions to XPath's built-in functions to enable XPath 1.0
expressions to access information from the process. The extensions are defined
in the standard BPEL4WS namespace http://schemas.xmlsoap.org/ws/2003/03/businessprocess/.
The prefix "bpws:" is
associated with this namespace.
Any qualified names used within
XPath expressions are resolved by using namespace declarations currently in
scope in the BPEL4WS document at the location of the expression.
The following functions are
defined by this specification:
bpws:getVariableProperty ('variableName', 'propertyName')
This function extracts global
property values from variables. The first argument names the source variable
for the data and the second is the qualified name (QName) of the global
property to select from that variable (see Message
Properties). If the given property does not appear in any of the
parts of the variable's message type, then the semantics of the process is
undefined. The return value of this function is a node set containing the
single node representing the property. If the given property definition selects
a node set of a size other than one, then the semantics of the process is
undefined.
bpws:getLinkStatus ('linkName')
This function returns a Boolean
indicating the status of the link (see Link Semantics). If the status of the
link is positive the value is true, and if the status is negative the value is
false. This function MUST NOT be used anywhere except in a join condition. The
linkName argument MUST refer to the name of an incoming link for the activity
associated with the join condition. These restrictions MUST be statically
enforced.
These BPEL4WS-defined extension
functions are available for use within all XPath 1.0 expressions.
The syntax of XPath 1.0
expressions for BPEL4WS is considered in the following paragraphs.
These are expressions that
conform to the XPath 1.0 Expr production where the evaluation results
in Boolean values.
These are expressions that
conform to the XPath 1.0 Expr production where the evaluation results
in values that are of the XML Schema types dateTime or date.
Note that XPath 1.0 is not XML Schema aware. As such, none of the built-in
functions of XPath 1.0 are capable of producing or manipulating dateTime or
date values. However, it is possible to write a constant (literal) that
conforms to XML Schema definitions and use that as a deadline value or to
extract a field from a variable (part) of one of these types and use that as a
deadline value. XPath 1.0 will treat that literal as a string literal, but the
result can be interpreted as a lexical representation of a dateTime or
date value.
These are expressions that
conform to the XPath 1.0 Expr production where the evaluation results
in values that are of the XML Schema type duration. The preceding
discussion about XPath 1.0's XML Schema unawareness applies here as well.
These are expressions that
conform to the XPath 1.0 Expr production where the evaluation results
in any XPath value type (string, number, or Boolean).
Expressions with operators are
restricted as follows:
·
All
numeric values including arbitrary constants are permitted with the equality or
relational operators (<, <=, =, !=, >=, >").
·
Values
of integral (short, int, long, unsignedShort, and so on) type including
constants are permitted in numeric expressions, provided that only integer
arithmetic is performed. In practice, this means that division is disallowed.
It is difficult to enforce this restriction in XPath 1.0 because XPath 1.0
lacks integral support for types. The restriction should be taken as a
statement of intent that will be enforced in the future when expression
languages with more refined type systems become available.
·
Only
equality operators (=, !=) are permitted when used with values of string type
including constants.
These restrictions reflect XPath
1.0 syntax and semantics. Future alternative standards in this space are
expected to provide stronger type systems and therefore support more nuanced
constraints. The restrictions are motivated by the fact that XPath general
expressions are meant to be used to perform business protocol-related computation
such as retry loops, line-item counts, and so on, that must be transparent in
the process definition. They are not meant to provide arbitrary computation.
This is the motivation for the constraint that numerical expressions deal only
with integer computation, and for disallowing arbitrary string manipulation
through expressions.
Business processes specify
stateful interactions involving the exchange of messages between partners. The
state of a business process includes the messages that are exchanged as well as
intermediate data used in business logic and in composing messages sent to
partners.
Variables provide the means for
holding messages that constitute the state of a business process. The messages
held are often those that have been received from partners or are to be sent to
partners. Variables can also hold data that are needed for holding state
related to the process and never exchanged with partners.
The type of each variable may be
a WSDL message type, an XML Schema simple type or an XML Schema element. The
syntax of the variables
declaration is:
<variables>
<variable name="ncname" messageType="qname"?
type=”qname”? element=”qname”?/>+
</variables>
The name of a variable should be
unique within its own scope. If a local variable has the same name and same
messageType/type/element as a variable defined in an enclosing scope, the local
variable will be used in local assignments and/or getVariableProperty
functions. It is not permitted to have variables with same name but different
messageType/type/element within an enclosing scope hierarchy. The behavior of
such variables is not defined.
The messageType, type or element attributes are used to specify the type of a variable. Exactly one of
these attributes must be used. Attribute messageType refers to a WSDL message type definition.
Attribute type refers to an
XML Schema simple type. Attribute element refers to an XML Schema element. An XML Schema complex type must
beassociated with an element to be used by a BPEL4WS variable.
An example of a variable
declaration using a message type declared in a WSDL document with the
targetNamespace "http://example.com/orders":
<variable xmlns:ORD="http://example.com/orders"
name="orderDetails" messageType="ORD:orderDetails"/>
Variables associated with message
types can be specified as input or output variables for invoke, receive, and
reply activities (see Invoking Web Service Operations
and Providing Web Service Operations). When an
invoke operation returns a fault message, this causes a fault in the current
scope. The fault variable in the corresponding fault handler is initialized
with the fault message received (see Scopes and Fault Handlers).
Each variable is declared within
a scope and is said to belong to that scope. Variables that belong to the
global process scope are called global variables. Variables may also belong to
other, non-global scopes, and such variables are called local variables. Each
variable is visible only in the scope in which it is defined and in all scopes
nested within the scope it belongs to. Thus, global variables are visible
throughout the process. It is possible to "hide" a variable in an
outer scope by declaring a variable with an identical name in an inner scope.
These rules are exactly analogous to those in programming languages with
lexical scoping of variables.
A global variable is in an
uninitialized state at the beginning of a process. A local variable is in an
uninitialized state at the start of the scope it belongs to. Note that
non-global scopes in general start and complete their behavior more than once
in the lifetime of the process instance they belong to. Variables can be
initialized by a variety of means including assignment and receiving a message.
Variables can be partially initialized with property assignment or when some
but not all parts in the message type of the variable are assigned values.
Copying data from one variable to
another is a common task within a business process. The assign activity can be used to copy data from
one variable to another, as well as to construct and insert new data using
expressions. The use of expressions is primarily motivated by the need to
perform simple computation (such as incrementing sequence numbers) that is
required for describing business protocol behavior. Expressions operate on
message selections, properties, and literal constants to produce a new value
for a variable property or selection. Finally, this activity can also be used
to copy endpoint references to and from partner links.
The assign assign contains one or more elementary
assignments.
<assign standard-attributes>
standard-elements
<copy>+
from-spec
to-spec
</copy>
</assign>
The assign activity copies a
type-compatible value from the source ("from-spec") to the
destination ("to-spec"). The from-spec MUST be one of the following forms except
for the opaque form available in abstract processes:
<from variable="ncname" part="ncname"?/>
<from partnerLink="ncname" endpointReference="myRole|partnerRole"/>
<from variable="ncname" property="qname"/>
<from expression="general-expr"/>
<from> ... literal value ... </from>
The to-spec MUST be one of the following forms:
<to variable="ncname" part="ncname"?/>
<to partnerLink="ncname"/>
<to variable="ncname" property="qname"/>
In the first from-spec and to-spec variants the variable attribute provides the name
of a variable. If the type of the variable is a WSDL messge type the optional
part attribute MAY be used to provide the name of a part within that variable.
When the variable is defined using XML Schema simple type or element, the part
attribute MUST NOT be used.
The second from-spec and to-spec variants allow dynamic manipulation of the
endpoint references associated with partner links. The value of the partnerLink
attribute is the name of a partnerLink declared in the process. In the case of
from-specs, the role must also be specified because a process might need to
communicate an endpoint reference corresponding to either its own role or the partner's
role within the partnerLink. The value “myRole” means that the
endpoint reference of the process with respect to that partnerLink is the
source, while the value “partnerRole” means that the
partner’s endpoint reference for the partnerLink is the source. For the
to-spec, the assignment is only possible to the partnerRole, hence there is no
need to specify the role. The type of the value used in partnerLink-style
from/to-specs is always an endpoint reference (see Partner
Link Types, Partner Links, and Endpoint References).
The third from-spec and to-spec variants allow explicit manipulation of message
properties (see Message Properties) occurring in
variables. The property forms are especially useful for abstract processes,
because they provide a way to clearly define how distinguished data elements in
messages are being used.
The fourth
("expression") from-spec variant allows processes to perform simple computations on properties and
variables (for example, increment a sequence number).
The fifth from-spec variant allows a literal value to be
given as the source value to assign to a destination. The type of the literal
value MUST be the type of the destination (to-spec). The type of the literal
value MAY be optionally indicated inline with the value by using XML Schema's
instance type mechanism (xsi:type).
For an assignment to be valid,
the data referred to by the from and to specifications MUST be of compatible
types. The following points make this precise:
·
The
from-spec is a variable of a WSDL message type and the to-spec is a variable of
a WSDL message type. In this case both variables MUST be of the same message
type, where two message types are said to be equal if their qualified names are
the same.
·
The
from-spec is a variable of a WSDL message type and the to-spec is not, or vice
versa. This is not legal because parts of variables, selections of variable
parts, or endpoint references cannot be assigned to/from variables of WSDL
message types directly.
·
In
all other cases, the types of the source and destination are XML Schema types
or elements, and the constraint is that the source value MUST possess the
element or type associated with the destination. Note that this does not
require the types associated with the source and destination to be the same. In
particular, the source type MAY be a subtype of the destination type. In the
case of variables defined by reference to an element, moreover, both the source
and the target MUST be the same element.
The semantics of a process in
which any of the matching constraints above is violated is undefined.
The example assumes the following
complex type definition in the namespace
"http://tempuri.org/bpws/example":
<complexType name="tAddress">
<sequence>
<element name="number" type="xsd:int"/>
<element name="street" type="xsd:string"/>
<element name="city" type="xsd:string"/>
<element name="phone">
<complexType>
<sequence>
<element name="areacode" type="xsd:int"/>
<element name="exchange" type="xsd:int"/>
<element name="number" type="xsd:int"/>
</sequence>
</complexType>
</element>
</sequence>
</complexType>
<element name = “address” type = “tAddress”/>
Assume that the following WSDL
message definition exists for the same target namespace:
<message name="person" xmlns:x="http://tempuri.org/bpws/example">
<part name="full-name" type="xsd:string"/>
<part name="address" element="x:address"/>
</message>
Also assume the following BPEL4WS
variable declarations:
<variable name="c1" messageType="x:person"/>
<variable name="c2" messageType="x:person"/>
<variable name="c3" element="x:address"/>
The example illustrates copying
one variable to another as well as copying a variable part to a variable of
compatible element type:
<assign>
<copy>
<from variable="c1"/>
<to variable="c2"/>
</copy>
<copy>
<from variable="c1" part = “address”/>
<to variable="c3"/>
</copy>
</assign>The information provided so far
suggests that the target for messages that are delivered to a business process
service is the WSDL port of the recipient service. This is an illusion because,
by their very nature, stateful business processes are instantiated to act in accordance with the history of
an extended interaction. Therefore, messages sent to such processes need to be
delivered not only to the correct destination port, but also to the correct instance of the business process that provides the
port. The infrastructure hosting the process must do this in a generic manner,
to avoid burdening every process implementation with the need to implement a
custom mechanism for instance routing. Messages, which create a new business
process instance, are a special case, as described in The
Lifecycle of a Business Process.
In the object-oriented world,
such stateful interactions are mediated by object references, which
intrinsically provide the ability to reach a specific object (instance) with
the right state and history for the interaction. This works reasonably well in
tightly coupled implementations where a dependency on the structure of the
implementation is normal. In the loosely coupled world of Web Services, the use
of such references would create a fragile web of implementation dependencies
that would not survive the independent evolution of business process
implementation details at each business partner. In this world, the answer is
to rely on the business data and communication protocol headers that define the
wirelevel contract between partners and to avoid the use of
implementation-specific tokens for instance routing whenever possible.
Consider the usual supply-chain
situation where a buyer sends a purchase order to a seller. Suppose that the
buyer and seller have a stable business relationship and are statically
configured to send documents related to the purchasing interaction to the URLs
associated with the relevant WSDL service ports. The seller needs to
asynchronously return an acknowledgement for the order, and the acknowledgement
must be routed to the correct business process instance at the buyer. The
obvious and standard mechanism to do this is to carry a business token in the
order message (such as a purchase order number) that is copied into the
acknowledgement for correlation. The token can be in the message envelope in a
header or in the business document (purchase order) itself. In either case, the
exact location and type of the token in the relevant messages is fixed and
instance independent. Only the value of the token is instance dependent.
Therefore, the structure and position of the correlation tokens in each message
can be expressed declaratively in the business process description. The BPEL4WS
notion of correlation set, described in the following section, provides this
feature. The declarative information allows a BPEL4WS-compliant infrastructure
to use correlation tokens to provide instance routing automatically.
The declarative specification of
correlation relies on declarative properties of messages. A property is simply
a "field" within a message identified by a query—by default the
query language is XPath 1.0. This is only possible when the type of the message
part or binding element is described by using an XML Schema. The use of
correlation tokens and endpoint references is restricted to message parts
described in this way. To be clear, the actual wire format of such types can
still be non-XML, for example, EDI flat files, based on different bindings for
port types.
During its lifetime, a business
process instance typically holds one or more conversations with partners
involved in its work. Conversations may be based on sophisticated transport
infrastructure that correlates the messages involved in a conversation by using
some form of conversation identity and routes them automatically to the correct
service instance without the need for any annotation within the business
process. However, in many cases correlated conversations involve more than two
parties or use lightweight transport infrastructure with correlation tokens
embedded directly in the application data being exchanged. In such cases, it is
often necessary to provide additional application-level mechanisms to match
messages and conversations with the business process instances for which they
are intended.
Correlation patterns can become
quite complex. The use of a particular set of correlation tokens does not, in
general, span the entire interaction between a service instance and a partner
(instance), but spans a part of the interaction. Correlated exchanges may nest
and overlap, and messages may carry several sets of correlation tokens. For
example, a buyer might start a correlated exchange with a seller by sending a
purchase order (PO) and using a PO number embedded in the
BPEL4WS addresses correlation
scenarios by providing a declarative mechanism to specify correlated groups of
operations within a service instance. A set of correlation tokens is defined as
a set of properties shared by all messages in the correlated group. Such a set
of properties is called a correlation set.
Correlation sets are declared
within scopes and associated with them in a manner that is analogous to
variable declarations. Each correlation set is declared within a scope and is
said to belong to that scope. Correlation sets that belong to the global
process scope are called global correlation sets. Correlation sets may also
belong to other, non-global scopes, and such correlation sets are called local
correlation sets. Each correlation set is only visible in the scope in which it
is defined and in all scopes nested within the scope it belongs to. Thus,
global correlation sets are visible throughout the process. It is possible to
"hide" a correlation set in an outer scope by declaring a correlation
set with an identical name in an inner scope.
A global correlation set is in an
uninitiated state at the beginning of a process. A local correlation set is in
an uninitiated state at the start of the scope it belongs to. Note that non-global
scopes in general start and complete their behavior more than once in the
lifetime of the process instance they belong to.
Correlation sets resemble
late-bound constants rather than variables in their semantics. The binding of a
correlation set is triggered by a specially marked message send or receive
operation. A correlation set can be initiated only once during the lifetime of
the scope it belongs to. Thus, a global correlation set can only be initiated
at most once during the lifetime of the process instance. Its value, once
initiated, can be thought of as an alias for the identity of the business
process instance. A local correlation set is available for binding each time
the corresponding scope starts, but once initiated must retain its value until
the scope completes.
In multiparty business protocols,
each participant process in a correlated message exchange acts either as the
initiator or as a follower of the exchange. The initiator process sends the
first message (as part of an operation invocation) that starts the
conversation, and therefore defines the values of the properties in the
correlation set that tag the conversation. All other participants are followers
that bind their correlation sets in the conversation by receiving an incoming
message that provides the values of the properties in the correlation set. Both
initiator and followers must mark the first activity in their respective groups
as the activity that binds the correlation set.
The examples in this section show
correlation being used on almost every messaging activity (receive, reply, and
invoke). This is because BPEL4WS does not assume the use of any sophisticated
conversational transport protocols for messaging. In cases where such protocols
are used, the explicit use of correlation in BPEL4WS can be reduced to those
activities that establish the conversational connections.
Each correlation set in BPEL4WS
is a named group of properties that, taken together, serve to define a way of
identifying an application-level conversation within a business protocol
instance. A given message can carry multiple correlation sets. After a
correlation set is initiated, the values of the properties for a correlation
set must be identical for all the messages in all the operations that carry the
correlation set and occur within the corresponding scope until its completion.
The semantics of a process in which this consistency constraint is violated is
undefined. Similarly undefined is the semantics of a process in which an
activity with the initiate attribute
set to no attempts to use a correlation set that
has not been previously initiated.
As the following examples
illustrate, a correlation set is initiated when the activity within which it is
used applies the attribute initiate="yes" to the set.
<correlationSets>?
<correlationSet name="ncname" properties="qname-list"/>+
</correlationSets>
Following is an extended example
of correlation. It begins by defining four message properties: customerID, orderNumber,
vendorID and invoiceNumber. All of these properties are defined as
part of the "http://example.com/supplyCorrelation.wsdl" namespace defined by the document.
<definitions name="properties"
targetNamespace="http://example.com/supplyCorrelation.wsdl"
xmlns:tns="http://example.com/supplyCorrelation.wsdl"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define correlation properties -->
<bpws:property name="customerID" type="xsd:string"/>
<bpws:property name="orderNumber" type="xsd:int"/>
<bpws:property name="vendorID" type="xsd:string"/>
<bpws:property name="invoiceNumber" type="xsd:int"/>
</definitions>
Note that these properties are
global names with known (simple) XMLSchema types. They are abstract in the
sense that their occurrence in messages needs to be separately specified (see Message Properties). The example continues by defining
purchase order and invoice messages and by using the concept of aliasing to map
the abstract properties to fields within the message data identified by
selection.
<definitions name="correlatedMessages"
targetNamespace="http://example.com/supplyMessages.wsdl"
xmlns:tns="http://example.com/supplyMessages.wsdl"
xmlns:cor="http://example.com/supplyCorrelation.wsdl"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!—define schema types for PO and invoice information -->
<types>
<xsd:schema>
<xsd:complexType name="PurchaseOrder">
<xsd:element name="CID" type="xsd:string"/>
<xsd:element name="order" type="xsd:int"/>
...
</xsd:complexType>
<xsd:complexType name="PurchaseOrderResponse">
<xsd:element name="CID" type="xsd:string"/>
<xsd:element name="order" type="xsd:int"/>
...
</xsd:complexType>
<xsd:complexType name="PurchaseOrderReject">
<xsd:element name="CID" type="xsd:string"/>
<xsd:element name="order" type="xsd:int"/>
<xsd:element name="reason" type="xsd:string"/>
...
</xsd:complexType>
<xsd:complexType name="Invoice">
<xsd:element name="VID" type="xsd:string"/>
<xsd:element name="invNum" type="xsd:int"/>
</xsd:complexType>
</xsd:schema>
</types>
<message name="POMessage">
<part name="PO" type="tns:PurchaseOrder"/>
</message>
<message name="POResponse">
<part name="RSP" type="tns:PurchaseOrderResponse"/>
</message>
<message name="POReject">
<part name="RJCT" type="tns:PurchaseOrderReject"/>
</message>
<message name="InvMessage">
<part name="IVC" type="tns:Invoice"/>
</message>
<bpws:propertyAlias propertyName="cor:customerID"
messageType="tns:POMessage" part="PO"
query="/PO/CID"/>
<bpws:propertyAlias propertyName="cor:orderNumber"
messageType="tns:POMessage" part="PO"
query="/PO/Order"/>
<bpws:propertyAlias propertyName="cor:vendorID"
messageType="tns:InvMessage" part="IVC"
query="/IVC/VID"/>
<bpws:propertyAlias propertyName="cor:invoiceNumber"
messageType="tns:InvMessage" part="IVC"
query="/IVC/InvNum"/>
...
</definitions>
Finally, the portType used is
defined, in a separate WSDL document.
<definitions name="purchasingPortType"
targetNamespace="http://example.com/puchasing.wsdl"
xmlns:smsg="http://example.com/supplyMessages.wsdl"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<portType name="PurchasingPT">
<operation name="SyncPurchase">
<input message="smsg:POMessage"/>
<output message="smsg:POResponse"/>
<fault name="tns:RejectPO" message="smsg:POReject"/>
</operation>
<operation name="AsyncPurchase">
<input message="smsg:POMessage"/>
</operation>
</portType>
<portType name="BuyerPT">
<operation name="AsyncPurchaseResponse">
<input message="smsg:POResponse"/>
<fault name="tns:RejectPO" message="smsg:POReject"/>
</operation>
<operation name="AsyncPurchaseReject">
<input message="smsg:POReject"/>
</operation>
</portType>
</definitions>
Both the properties and their
mapping to purchase order and invoice messages will be used in the following correlation
examples.
<correlationSets
xmlns:cor="http://example.com/supplyCorrelation.wsdl">
<!-- Order numbers are particular to a customer,
this set is carried in application data -->
<correlationSet name="PurchaseOrder"
properties="cor:customerID cor:orderNumber"/>
<!-- Invoice numbers are particular to a vendor,
this set is carried in application data -->
<correlationSet name="Invoice"
properties="cor:vendorID cor:invoiceNumber"/>
</correlationSets>
Correlation set names are used in
invoke, receive, and reply activities (see Invoking Web Service Operations
and Providing Web Service Operations), in the onMessage branches of
pick activities, and in the onMessage variant of event handlers (see Pick
and Message Events). These sets are used to indicate which correlation
sets (i.e., the corresponding property sets) occur in the messages being sent
and received. The initiate attribute
is used to indicate whether the set is being initiated. When the attribute is
set to "yes" the set is initiated with the values of the properties
occurring in the message being sent or received. Finally, in the case of
invoke, when the operation invoked is synchronous request/response, a pattern attribute is used to indicate whether the
correlation applies to the outbound (request) message, the inbound (response)
message, or both. These ideas are explained in more detail in the context of
the use of correlation in the rest of this example.
A message can carry the tokens of
one or more correlation sets. The first example shows an interaction in which a
purchase order is received in a one-way inbound request and a confirmation
including an invoice is sent in the asynchronous response. The PurchaseOrder correlationSet is used in both activities
so that the asynchronous response can be correlated to the request at the
buyer. The receive activity initiates the PurchaseOrder correlationSet. The buyer is therefore
the initiator and the receiving business process is a follower for this
correlationSet. The invoke activity sending the asynchronous response also initiates a new
correlationSet Invoice. The business process is the initiator of this
correlated exchange and the buyer is a follower. The response message is thus a
part of two separate conversations, and forms the bridge between them.
In the following, the prefix SP: represents the namespace "http://example.com/puchasing.wsdl".
<receive partnerLink="Buyer" portType="SP:PurchasingPT"
operation="AsyncPurchase"
variable="PO">
<correlations>
<correlation set="PurchaseOrder" initiate="yes">
</correlations>
</receive>
<invoke partnerLink="Buyer" portType="SP:BuyerPT"
operation="AsyncPurchaseResponse" inputVariable="POResponse">
<correlations>
<correlation set="PurchaseOrder" initiate="no" pattern="out">
<correlation set="Invoice" initiate="yes" pattern="out">
</correlations>
</invoke>
Alternatively, the response might
have been a rejection (such as an "out-of-stock" message), which in
this case terminates the conversation correlated by the correlationSet PurchaseOrder without starting a new one correlated
with Invoice. Note that the initiate attribute is missing. It therefore has
the default value of "no".
<invoke partnerLink="Buyer" portType="SP:BuyerPT"
operation="AsyncPurchaseReject" inputVariable="POReject">
<correlations>
<correlation set="PurchaseOrder" pattern="out">
</correlations>
</invoke>
The use of correlation with
synchronous Web Service invocation is illustrated by the alternative
synchronous purchasing operation used by an invoke activity used in the buyer's
business process.
<invoke partnerLink="Seller" portType="SP:PurchasingPT"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
<correlations>
<correlation set="PurchaseOrder" initiate="yes" pattern="out">
<correlation set="Invoice" initiate="yes" pattern="in">
</correlations>
<catch faultName="SP:RejectPO" faultVariable="POReject">
<!-- handle the fault -->
</catch>
</invoke>
Note that an invoke consists of two messages: an outgoing
request message and an incoming reply message. The correlation sets applicable
to each message must be separately considered because they can be different. In
this case the PurchaseOrder
correlation applies to the outgoing request that initiates it, while the Invoice correlation applies to the incoming reply
and is initiated by the reply. Because the PurchaseOrder correlation is initiated by an outgoing
message, the buyer is the initiator of that correlation but a follower of the Invoice correlation because the values of the
correlation properties for Invoice are initiated by the seller in the reply
received by the buyer.
Each activity has optional
standard attributes: a name, a join condition, and an indicator whether a join
fault should be suppressed if it occurs. A join condition is used to specify
requirements about concurrent paths reaching at an activity. See Flow for a full discussion of the last two attributes.
The default value of suppressJoinFailure is no.
name="ncname"?
joinCondition="bool-expr"?
suppressJoinFailure="yes|no"?>
The value of the joinCondition
attribute is a Boolean-valued expression in the expression language indicated
for this document (see Expressions). The default
value of the join condition for the default expression language XPath is the
logical OR of the link status of all incoming links of this activity.
Each BPEL4WS activity has
optional nested standard elements <source> and <target>. The use of
these elements is required for establishing synchronization relationships
through links (see Flow). Each link is defined
independently and given a name. The link name is used as value of the linkName
attribute of the <source> element. An activity MAY declare itself to be
the source of one or more links by including one or more <source>
elements. Each <source> element MUST use a distinct link name. Similarly,
an activity MAY declare itself to be the target of one or more links by
including one or more <target> elements. Each <source> element
associated with a given activity MUST use a link name distinct from all other
<source> elements at that activity. Each <target> element associated
with a given activity MUST use a link name distinct from all other
<target> elements at that activity. Each <source> element MAY
optionally specify a transition condition that functions as a guard for
following this specified link (see Flow). If the transition condition is omitted,
it is deemed to be present with the constant value true.
<source linkName="ncname" transitionCondition="bool-expr"?/>*
<target linkName="ncname"/>*Web Services provided by partners
(see Partner Link Types, Partner Links, and Endpoint
References) can be used to perform work in a BPEL4WS business
process. Invoking an operation on such a service is a basic activity. Recall
that such an operation can be a synchronous request/response or an asynchronous
one-way operation. BPEL4WS uses the same basic syntax for both with some
additional options for the synchronous case.
An asynchronous invocation
requires only the input variable of the operation because it does not expect a
response as part of the operation (see Providing Web
Service Operations). A synchronous invocation requires both an input
variable and an output variable. One or more correlation sets can be specified
to correlate the business process instance with a stateful service at the
partner’s side (see Correlation). However,
these attributes are both syntactically optional since they are absolutely
required only in executable processes.
In the case of a synchronous
invocation, the operation might return a WSDL fault message. This results in a
BPEL4WS fault. Such a fault can be caught locally by the activity, and in this
case the specified activity will be performed. If a fault is not caught locally
by the activity it is thrown to the scope that encloses the activity (see Scopes and Fault Handlers).
Note that a WSDL fault is
identified in BPEL4WS by a qualified name formed by the target namespace of the
corresponding portType and the fault name. This uniform naming mechanism must
be followed even though it does not accurately match WSDL’s faultnaming
model. Because WSDL does not require that fault names be unique within the
namespace where the service operation is defined, all faults sharing a common
name and defined in the same namespace are indistinguishable in BPEL4WS. In
WSDL 1.1 it is necessary to specify a portType name, an operation name, and the
fault name to uniquely identify a fault. This limits the ability to use
fault-handling mechanisms to deal with invocation faults. This is an important
shortcoming of the WSDL fault model that will be removed in future versions of
WSDL.
Finally, an activity can be
associated with another activity that acts as its compensation action. This
compensation handler can be invoked either explicitly or by the default
compensation handler of the enclosing scope (see Scopes
and Compensation Handlers).
Semantically, the specification
of local fault and/or compensation handlers is equivalent to the presence of an
implicit scope immediately enclosing the activity and providing those handlers.
The name of such an implicit scope is always the same as the name of the
activity it encloses.
<invoke partnerLink="ncname" portType="qname" operation="ncname"
inputVariable="ncname"? outputVariable="ncname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?
pattern="in|out|out-in"/>+
</correlations>
<catch faultName="qname" faultVariable="ncname"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
<compensationHandler>?
activity
</compensationHandler>
</invoke>
See Correlation
for an explanation of the correlation semantics. The following example shows an
invocation with a nested compensation handler. Other examples are shown
throughout the specification.
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
<compensationHandler>
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="CancelPurchase"
inputVariable="getResponse"
outputVariable="getConfirmation">
</compensationHandler>
</invoke>A business process provides
services to its partners through receive activities and corresponding reply
activities. A receive activity specifies the partner link it expects to receive
from, and the port type and operation that it expects the partner to invoke. In
addition, it may specify a variable that is to be used to receive the message
data received. However, this attribute is syntactically optional since it is
absolutely required only in executable processes.
In addition, receive activities
play a role in the lifecycle of a business process. The only way to instantiate
a business process in BPEL4WS is to annotate a receive activity with the createInstance attribute set to "yes" (see Pick for a variant). The default value of this
attribute is "no". A receive activity annotated in this way MUST be an initial activity in the process,
that is, the only other basic activities may potentially be performed prior to
or simultaneously with such a receive activity MUST be similarly annotated receive activities.
It is permissible to have the createInstance attribute set to "yes" for a
set of concurrent initial activities. In this case the intent is to express the
possibility that any one of a set of required inbound messages can create the
process instance because the order in which these messages arrive cannot be
predicted. All such receive activities MUST use the same correlation sets (see Correlation).
Compliant implementations MUST ensure that only one of the inbound messages
carrying the same correlation set tokens actually instantiates the business
process (usually the first one to arrive, but this is implementation
dependent). The other incoming messages in the concurrent initial set MUST be
delivered to the corresponding receive activities in the already created instance.
A business process instance MUST
NOT simultaneously enable two or more receive activities for the same partnerLink, portType,
operation and correlation set(s). Note that receive is a blocking activity in the sense that it will
not complete until a matching message is received by the process instance. The
semantics of a process in which two or more receive actions for the same partnerLink, portType,
operation and correlation set(s) may be simultaneously enabled is undefined.
For the purposes of this constraint, an onMessage clause in a pick and an onMessage event handler are equivalent to
a receive (see Pick
and Message Events).
<receive partnerLink="ncname" portType="qname" operation="ncname"
variable="ncname"? createInstance="yes|no"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?>+
</correlations>
</receive>
A reply activity is used to send a response to a request
previously accepted through a receive activity. Such responses are only meaningful for synchronous interactions.
An asynchronous response is always sent by invoking the corresponding one-way
operation on the partner link. A reply activity may specify a variable that contains the message data to be sent
in reply. However, this attribute is syntactically optional since it is
absolutely required only in executable processes.
The correlation between a request
and the corresponding reply is based on the constraint that more than one
outstanding synchronous request from a specific partner link for a particular
portType, operation and correlation set(s) MUST NOT be outstanding
simultaneously. The semantics of a process in which this constraint is violated
is undefined. For the purposes of this constraint, an onMessage clause in a pick is equivalent to a receive (see Pick).
Moreover, a reply activity must always be preceded by a receive activity for the same partner link,
portType and (request/response) operation, such that no reply has been sent for
that receive activity. The semantics of a process in
which this constraint is violated is undefined.
<reply partnerLink="ncname" portType="qname" operation="ncname"
variable="ncname"? faultName="qname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?>+
</correlations>
</reply>
Note that the <reply>
activity corresponding to a given request has two potential forms. If the
response to the request is normal, the faultName attribute is not used and the variable attribute, when present, will indicate a
variable of the normal response message type. If, on the other hand, the
response indicates a fault, the faultName attribute is used and the variable attribute, when present, will indicate a variable of the message type for
the corresponding fault.
Variable update occurs through
the assignment activity, which is described in Assignment.
The throw activity can be used when a business process
needs to signal an internal fault explicitly. Every fault is required to have a
globally unique QName. The throw activity is required to provide such a name for the fault and can
optionally provide a variable of data that provides further information about
the fault. A fault handler can use such data to analyze and handle the fault
and also to populate any fault messages that need to be sent to other services.
BPEL4WS does not require fault
names to be defined prior to their use in a throw element. An application or
process-specific fault name can be directly used by using an appropriate QName
as the value of the faultName attribute and providing a variable with the fault
data if required. This provides a very lightweight mechanism to introduce
application-specific faults.
<throw faultName="qname" faultVariable="ncname"? standard-attributes>
standard-elements
</throw>
A simple example of a throw
activity that does not provide a variable of fault data is:
<throw xmlns:FLT="http://example.com/faults" faultName="FLT:OutOfStock"/>The wait activity allows a business process to specify a
delay for a certain period of time or until a certain deadline is reached (see Expressions for the grammar of duration expressions
and deadline expressions).
<wait (for="duration-expr" | until="deadline-expr") standard-attributes>
standard-elements
</wait>
A typical use of this activity is
to invoke an operation at a certain time (in this case a constant, but more
typically an expression dependent on process state):
<sequence>
<wait until="'2002-12-24T18:00+01:00'"/>
<invoke partnerLink="CallServer" portType="AutomaticPhoneCall"
operation="TextToSpeech"
inputVariable="seasonalGreeting">
</invoke>
</sequence>Structured activities prescribe
the order in which a collection of activities take place. They describe how a
business process is created by composing the basic activities it performs into
structures that express the control patterns, data flow, handling of faults and
external events, and coordination of message exchanges between process
instances involved in a business protocol.
The structured activities of
BPEL4WS include:
·
Ordinary
sequential control between activities is provided by sequence, switch, and while.
·
Concurrency
and synchronization between activities is provided by flow.
·
Nondeterministic
choice based on external events is provided by pick.
Structured activities can be used
recursively in the usual way. A key point to understand is that structured
activities can be nested and combined in arbitrary ways. This provides a
somewhat unusual but very attractive free blending of the graph-like and
program-like control regimes that have traditionally been seen as alternatives
rather than orthogonal composable features. A simple example of such blended
usage is found in the Initial Example.
It is important to emphasize that
the word activity is used
throughout the following to include both basic and structured activities.
A sequence activity contains one or more activities
that are performed sequentially, in the order in which they are listed within
the <sequence> element, that is, in lexical order. The sequence activity completes when the final activity
in the sequence has completed.
<sequence standard-attributes>
standard-elements
activity+
</sequence>
Example:
<sequence>
<flow>
...
</flow>
<scope>
...
</scope>
<pick>
...
</pick>
</sequence>The switch structured activity supports conditional behavior
in a pattern that occurs quite often. The activity consists of an ordered list
of one or more conditional branches defined by case elements, followed optionally by an otherwise branch. The case branches of the switch are considered in the order in which they appear.
The first branch whose condition holds true is taken and provides the activity
performed for the switch. If no branch with a condition is taken, then the otherwise branch is taken. If the otherwise branch is not explicitly specified, then
an otherwise branch with an empty activity is deemed to be present. The switch activity is complete when the activity of
the selected branch completes.
<switch standard-attributes>
standard-elements
<case condition="bool-expr">+
activity
</case>
<otherwise>?
activity
</otherwise>
</switch>
Example:
<switch xmlns:inventory="http://supply-chain.org/inventory"
xmlns:FLT="http://example.com/faults">
<case condition= "bpws:getVariableProperty(stockResult,level) > 100">
<flow>
<!-- perform fulfillment work -->
</flow>
</case>
<case condition="bpws:getVariableProperty(stockResult,level) >= 0">
<throw faultName="FLT:OutOfStock"
variable="RestockEstimate"/>
</case>
<otherwise>
<throw faultName="FLT:ItemDiscontinued"/>
</otherwise>
</switch>The while activity supports repeated performance of a
specified iterative activity. The iterative activity is performed until the
given Boolean while condition no longer holds true.
<while condition="bool-expr" standard-attributes>
standard-elements
activity
</while>
Example:
...
<variable name="orderDetails" type="xsd:integer"/>
...
<while condition=
"bpws:getVariableData(orderDetails) > 100">
<scope>
...
</scope>
</while>The pick activity awaits the occurrence of one of a set of
events and then performs the activity associated with the event that occurred.
The occurrence of the events is often mutually exclusive (the process will
either receive an acceptance message or a rejection message, but not both). If
more than one of the events occurs, then the selection of the activity to
perform depends on which event occurred first. If the events occur almost
simultaneously, there is a race and the choice of activity to be performed is
dependent on both timing and implementation.
The form of pick is a set of branches of the form
event/activity, and exactly one of the branches will be selected based on the
occurrence of the event associated with it before any others. Note that after
the pick activity has accepted an event for handling, the other events are no
longer accepted by that pick. The possible events are the arrival of some message in the form of the
invocation of an inbound one-way or request/response operation, or an
"alarm" based on a timer (in the sense of an alarm clock).
A special form of pick is used when the creation of an instance
of the business process could occur as a result of receiving one of a set of
possible messages. In this case, the pick itself has a createInstance attribute
with a value of yes (the default
value of the attribute is no). In such a case, the events in the pick must all be inbound messages and each of
those is equivalent to a receive with the attribute "createInstance=yes". No alarms are permitted for this special case.
Each pick activity MUST include at least one onMessage event. The semantics of the onMessage event is identical to a receive activity
regarding the optional nature of the variable attribute and the constraint
regarding simultaneous enablement of conflicting receive actions. For the
latter, recall that the semantics of a process in which two or more receive actions for the same partner link,
portType, operation and correlation set(s) may be simultaneously enabled is
undefined (see Providing Web Service Operations).
Enablement of each onMessage handler is
equivalent to enablement of the corresponding receive activity for the purposes of this constraint.
<pick createInstance="yes|no"? standard-attributes>
standard-elements
<onMessage partnerLink="ncname" portType="qname"
operation="ncname" variable="ncname"?>+
<correlations>?
<correlation set="ncname" initiate="yes|no"?>+
</correlations>
activity
</onMessage>
<onAlarm (for="duration-expr" | until="deadline-expr")>*
activity
</onAlarm>
</pick>
The pick activity completes when one of the branches is
triggered by the occurrence of its associated event and the corresponding
activity completes. The following example shows a typical usage of pick. Such a
pick activity can occur in a loop that is accepting line items for a large order,
but a completion action is enabled as an alternative event.
<pick>
<onMessage partnerLink="buyer"
portType="orderEntry"
operation="inputLineItem"
variable="lineItem">
<!-- activity to add line item to order -->
</onMessage>
<onMessage partnerLink="buyer"
portType="orderEntry"
operation="orderComplete"
variable="completionDetail">
<!-- activity to perform order completion -->
</onMessage>
<!-- set an alarm to go after 3 days and 10 hours -->
<onAlarm for="'P3DT10H'">
<!-- handle timeout for order completion -->
</onAlarm>
</pick>The flow construct provides concurrency and
synchronization. The grammar for flow is:
<flow standard-attributes>
standard-elements
<links>?
<link name="ncname">+
</links>
activity+
</flow>
The standard
attributes and standard elements for
activities nested within a flow are especially significant because the standard attributes and elements
primarily exist to provide flow-related semantics to activities.
The most fundamental semantic
effect of grouping a set of activities in a flow is to enable concurrency. A flow completes when all of the activities in
the flow have completed. Completion of an activity
in a flow includes the possibility that it will be skipped if its enabling
condition turns out to be false (see Dead-Path-Elimination).
Thus the simplest use of flow is equivalent to a nested concurrency construct. In the following example,
the two invoke activities are enabled to start concurrently as soon as the flow is started. The completion of the flow occurs after both the seller and the
shipper respond (assuming the invoke operations were synchronous
request/response). The bank is invoked only after the flow completes.
<sequence>
<flow>
<invoke partnerLink="Seller" .../>
<invoke partnerLink="Shipper" .../>
</flow>
<invoke partnerLink="Bank" .../>
</sequence>
More generally, a flow activity
creates a set of concurrent activities directly nested within it. It further
enables expression of synchronization dependencies between activities that are
nested directly or indirectly within it. The link construct is used to express these
synchronization dependencies. A link has a name and all the links of a flow activity MUST be defined separately
within the flow activity. The standard source and target elements of an activity are used to link two activities. The source of the
link MUST specify a source element specifying the link's name and the target of the link MUST specify
a target element specifying the link's name. The
source activity MAY also specify a transition condition through the transitionCondition attribute of the source element. If the transitionCondition attribute is omitted, it is deemed to be
present with a value of "true". Every link declared within a flow activity MUST
have exactly one activity within the flow as its source and exactly one
activity within the flow as its target. The source and target of a link MAY be
nested arbitrarily deeply within the (structured) activities that are directly
nested within the flow, except for the boundary-crossing restrictions.
The following example shows that
links can cross the boundaries of structured activities. There is a link named
"CtoD" that starts at activity C in sequence Y and ends at activity
D, which is directly nested in the enclosing flow. The example further
illustrates that sequence X must be performed prior to sequence Y because X is
the source of the link named "XtoY" that is targeted at sequence Y.
<flow>
<links>
<link name="XtoY"/>
<link name="CtoD"/>
</links>
<sequence name="X">
<source linkName="XtoY"/>
<invoke name="A" .../>
<invoke name="B" .../>
</sequence>
<sequence name"Y">
<target linkName="XtoY"/>
<receive name="C" ...>
<source linkName="CtoD"/>
</receive>
<invoke name="E" .../>
</sequence>
<invoke partnerLink="D" ...>
<target linkName="CtoD"/>
</invoke>
</flow>
In general, a link is said to
cross the boundary of a
syntactic construct if the source activity for the link is nested within the
construct but the target activity is not, or vice versa, if the target activity
for the link is nested within the construct but the source activity is not.
A link MUST NOT cross the
boundary of a while activity, a serializable scope, an event handler or a
compensation handler (see Scopes for the
specification of event, fault and compensation handlers). In addition, a link
that crosses a fault-handler boundary MUST be outbound, that is, it MUST have
its source activity within the fault handler and its target activity within a
scope that encloses the scope associated with the fault handler. Finally, a
link MUST NOT create a control cycle, that is, the source activity must not
have the target activity as a logically preceding activity, where an activity A
logically precedes an activity B if the initiation of B semantically requires
the completion of A. Therefore, directed graphs created by links are always
acyclic.
In the rest of this section, the
links for which activity A is the source will be referred to as A's outgoing links, and the links for which activity A
is the target will be referred to as A's incoming links. If activity X is the target of a
link that has activity Y as the source, X has a synchronization dependency on Y.
Every activity that is the target
of a link has an implicit or explicit joinCondition attribute associated with it. This
applies even when an activity has exactly one incoming link. If the explicit joinCondition is missing, the implicit condition
requires the status of at least one incoming link to be positive (see below for an explanation of link
status). A join condition is a Boolean expression (see Expressions).
The expression for a join condition for an activity MUST be constructed using
only Boolean operators and the bpws:getLinkStatus function (see Expressions)
applied to incoming links at the activity.
Without considering links, the
semantics of business processes, scopes, and structured activities determine
when a given activity is ready to start. For example, the second activity in a
sequence is ready to start as soon as the first activity completes. An activity
that defines the behavior of a branch in a switch is ready to start if and when
that branch is chosen. Similarly, an activity nested directly within a flow is
ready to start as soon as the flow itself starts, because flow is fundamentally
a concurrency construct.
If an activity that is ready to
start in this sense has incoming links, then it does not start until the status
of all its incoming links has been determined and the (implicit or explicit)
join condition associated with the activity has been evaluated. The precise
semantics of link status evaluation are as follows:
When activity A completes, the
following steps are performed to determine the effect of the synchronization
links on other activities:
·
Determine
the status of all outgoing links for A. The status will be either positive or negative. To determine the status for each link
its transitionCondition is evaluated. Note that the evaluation is
carried out with the actual values of the variables referenced in the
transition condition expression. If some of the variables are modified in a
concurrent behavior path, the result of the transition condition evaluation may
depend nondeterministically on the timing of behavior among concurrent
activities. If the value is true the status is positive, otherwise it is negative.
·
For
each activity B that has a synchronization dependency on A, check whether:
o B is ready to start (except for its
dependency on incoming links) in the sense described above.
o The status of all incoming links for B has
been determined.
·
If
both these conditions are true, then evaluate the join condition for B. If the
join condition evaluates to false, a standard bpws:joinFailure fault is thrown, otherwise activity B is
started.
If, during the performance of
structured activity S, the semantics of S dictate that activity X nested within
S will not be performed as part of the behavior of S, then the status of all
outgoing links from X is set to negative. An example is an activity within a
branch that is not taken in a switch activity, or activities that were not
completed in a scope in which processing was halted due to a fault, including a
bpws:joinFailure (see Scopes
and Compensation Handlers).
Note that in general multiple
target activities will be enabled based on the completion of an activity with
multiple outgoing links; because of this, such an activity is often called a
fork activity.
In cases where the control flow
is largely defined by networks of links, the normal interpretation of a false
join condition for activity A is that A should not be performed, rather than
that a fault has occurred. Moreover, there is a need to propagate the
consequences of this decision by assigning a negative status to the outgoing
links for A. BPEL4WS makes it easy to express these semantics by using an
attribute suppressJoinFailure
on an activity. A value of "yes" for this attribute has the effect of
suppressing the bpws:joinFailure
fault for the activity and all nested activities, except where the effect is
overridden by using the suppressJoinFailure attribute with a value of "no" in a
nested activity. Suppressing the bpws:joinFailure is equivalent to the fault being logically caught
by a special default handler attached to an implicit scope that immediately
encloses just the activity with the join condition. The default handler
behavior is an empty activity, that
is, the handler suppresses the fault and does nothing about it. However,
because the activity with the join condition was not performed, its outgoing
links are automatically assigned a negative status according to the rules of Link Semantics. Thus within an activity with the value
of the suppressJoinFailure attribute set to "yes", the
semantics of a join condition that evaluates to false are to skip the associated
activity and to set the status of all outgoing links from that activity to
negative. This is called dead-pathelimination because in a graph-like
interpretation of networks of links with transition conditions, these semantics
have the effect of propagating negative link status transitively along entire
paths formed by consecutive links until a join condition is reached that
evaluates to true.
Note that the name of the implicit scope (created to
suppress the bpws:joinFailure) that immediately encloses an activity with a
join condition is exactly the same as the name of the activity itself. In case
this is an invoke activity (see Invoking Web Service
Operations) with an inlined fault or compensation handler, the
implicit scope for the fault and compensation handlers is merged with the
implicit scope described here, which adds an additional fault handler for the bpws:joinFailure.
The default value of the suppressJoinFailure attribute is "no". This is to
avoid unexpected behavior in simple use cases where complex graphs are not
involved and links without transition conditions are used for synchronization.
The designers of such use cases are likely to be naive about link semantics and
are likely to be surprised by the consequences of a default interpretation that
suppresses a well-defined fault. For example, consider the interpretation of
the Initial Example with the suppressJoinFailure attribute set to "yes". Suppose further that the invocations of
the shippingProvider are enclosed in a scope that provides a
fault handler (see Scopes and Fault
Handlers). If one of these invocations were to fault, the status of
the outgoing link from the invocation would be negative, and the (implicit)
join condition at the target of the link would be false, but the resulting bpws:joinFailure would be implicitly suppressed and the
target activity would be silently skipped within the sequence instead of
causing the expected fault.
If universal suppression of the bpws:joinFailure is desired, it is easy to achieve by
using the suppressJoinFailure
attribute with a value of "yes" in the overall process element at the root of the business process
definition.
In the following example, the
activities with the names getBuyerInformation, getSellerInformation, settleTrade,
confirmBuyer, and confirmSeller are nodes of a graph defined through the
flow activity. The following links are defined:
·
The
link named buyToSettle starts
at getBuyerInformation (specified through the corresponding source element nested in getBuyerInformation) and ends at settleTrade (specified through the corresponding
target element nested in settleTrade).
·
The
link named sellToSettle starts
at getSellerInformation and ends at settleTrade.
·
The
link named toBuyConfirm starts
at settleTrade and ends at confirmBuyer.
·
The
link named toSellConfirm starts
at settleTrade and ends at confirmSeller.
Based on the graph structure
defined by the flow, the activities getBuyerInformation and getSellerInformation can run concurrently. The settleTrade activity is not performed before both of
these activities are completed. After settleTrade completes the two activities, confirmBuyer and confirmSeller are performed concurrently again.
<flow suppressJoinFailure="yes">
<links>
<link name="buyToSettle"/>
<link name="sellToSettle"/>
<link name="toBuyConfirm"/>
<link name="toSellConfirm"/>
</links>
<receive name="getBuyerInformation">
<source linkName="buyToSettle"/>
</receive>
<receive name="getSellerInformation">
<source linkName="sellToSettle"/>
</receive>
<invoke name="settleTrade"
joinCondition="bpws:getLinkStatus('buyToSettle') and
bpws:getLinkStatus('sellToSettle')">
<target linkName="getBuyerInformation"/>
<target linkName="getSellerInformation"/>
<source linkName="toBuyConfirm"/>
<source linkName="toSellConfirm"/>
</invoke>
<reply name="confirmBuyer">
<target linkName="toBuyConfirm"/>
</reply>
<reply name="confirmSeller">
<target linkName="toSellConfirm"/>
</reply>
</flow>Links can cross the boundaries of
structured activities. When this happens, care must be taken to ensure the
intended behavior of the business process. The following example illustrates the
behavior when links target activities within structured constructs.
The following flow is intended to
perform the sequence of activities A, B, and C. Activity B has a
synchronization dependency on the two activities X and Y outside of the
sequence, that is, B is a target of links from X and Y. The join condition at B
is missing, and therefore implicitly assumed to be the default, which is the
disjunction of the status of the links targeted to B. The condition is
therefore true if at least one of the incoming links has a positive status. In
this case that condition reduces to the Boolean condition P(X,B) OR P(Y,B) based on the transition conditions on the
links.
In the flow, the sequence S and
the two receive activities X and Y are all concurrently enabled to start when
the flow starts. Within S, after activity A is completed, B cannot start until
the status of its incoming links from X and Y is determined and the implicit
join condition is evaluated. When activities X and Y complete, the join
condition for B is evaluated.
Suppose that the expression P(X,B) OR P(Y,B) evaluates to false. In this case, the
standard fault bpws:joinFailure
will be thrown, because the environmental attribute suppressJoinFailure is set to "no". Thus the
behavior of the flow is interrupted and neither B nor C will be performed.
If, on the other hand, the
environmental attribute suppressJoinFailure is set to "yes", then B will be skipped
but C will be performed because the bpws:joinFailure will be suppressed by the implicit scope associated
with B.
<flow suppressJoinFailure="no">
<links>
<link name="XtoB"/>
<link name="YtoB"/>
</links>
<sequence name="S">
<receive name="A" ...>
...
</receive>
<receive name="B" ...>
<target linkName="XtoB"/>
<target linkName="YtoB"/>
...
</receive>
<receive name="C" ...>
...
</receive>
</sequence>
<receive name="X" ...>
<source linkName="XtoB" transitionCondition="P(X,B)"/>
...
</receive>
<receive name="Y" ...>
<source linkName="YtoB" transitionCondition="P(Y,B)"/>
...
</receive>
</flow>
Finally, assume that the
preceding flow is slightly rewritten by linking A, B, and C through links (with
transition conditions with constant truth-value of "true") instead of
putting them into a sequence. Now, B and thus C will always be performed.
Because the join condition is a disjunction and the transition condition of
link AtoB is the constant "true", the join condition will always
evaluate to "true", independent from the values of P(X,B) and P(Y,B).
<flow suppressJoinFailure="no">
<links>
<link name="AtoB"/>
<link name="BtoC"/>
<link name="XtoB"/>
<link name="YtoB"/>
</links>
<receive name="A">
<source linkName="AtoB"/>
</receive>
<receive name="B">
<target linkName="AtoB"/>
<target linkName="XtoB"/>
<target linkName="YtoB"/>
<source linkName="BtoC"/>
</receive>
<receive name="C">
<target linkName="BtoC"/>
</receive>
<receive name="X">
<source linkName="XtoB" transitionCondition="P(X,B)"/>
</receive>
<receive name="Y">
<source linkName="YtoB" transitionCondition="P(Y,B)"/>
</receive>
</flow>The behavior context for each
activity is provided by a scope. A scope can provide fault
handlers, event handlers, a compensation handler, data variables, and
correlation sets.
All scope elements are
syntactically optional and some have default semantics when omitted. The syntax
and semantics of scopes are explained in detail below.
<scope variableAccessSerializable="yes|no" standard-attributes>
standard-elements
<variables>?
...
</variables>
<correlationSets>?
...
</correlationSets>
<faultHandlers>?
...
</faultHandlers>
<compensationHandler>?
...
</compensationHandler>
<eventHandlers>?
...
</eventHandlers>
activity
</scope>
Each scope has a primary activity
that defines its normal behavior. The primary activity can be a complex
structured activity, with many nested activities within it to arbitrary depth.
The scope is shared by all the nested activities. In the following example, the
scope has a primary flow activity, which contains two concurrent invoke activities. Either of the
invoke activities can receive one or more types of fault responses. The fault
handlers for the scope are shared by both invoke activities and can be used to
catch the faults caused by the possible fault responses.
<scope>
<faultHandlers>?
...
</faultHandlers>
<flow>
<invoke partnerLink="Seller" portType="Sell:Purchasing"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse"/>
<invoke partnerLink="Shipper"
portType="Ship:TransportOrders"
operation="OrderShipment"
inputVariable="sendShipOrder"
outputVariable="shipAck"/>
</flow>
</scope>
A scope can have defined
variables that live only within the scope. For further information see the
chapter about data handling.
Business processes are often of
long duration and use asynchronous messages for communication. They also
manipulate sensitive business data in back-end databases and line-of-business
applications. Error handling in this environment is both difficult and business
critical. The use of ACID transactions is usually limited to local updates
because of trust issues and because locks and isolation cannot be maintained
for the long periods during which technical and business errors and fault
conditions can occur in a business process instance. As a result, the overall
business transaction can fail or be cancelled after many ACID transactions have
been committed during its progress, and the partial work done must be undone as
best as possible. Error handling in business processes therefore relies heavily
on the well-known concept of compensation, that is, application-specific activities that attempt to reverse the
effects of a previous activity that was carried out as part of a larger unit of
work that is being abandoned. There is a long history of work in this area
regarding the use of Sagas [Sagas]
and open nested transactions [Trends].
BPEL4WS provides a variant of such a compensation protocol by providing the
ability for flexible control of the reversal. BPEL4WS achieves this by
providing the ability to define fault handling and compensation in an
application-specific manner, resulting in a feature called Long-Running
(Business) Transactions (LRTs).
It is important to understand
that the notion of LRT described here is meant to be used purely within a
platform-specific implementation. There is no prescribed requirement that the
business process be distributed or span multiple vendors and platforms. For
such environments, it is expected that the WS-Transaction specification [WS-Transaction] would be
utilized to register participants interested in the reversal notifications
provided by the LRT implementation. See Appendix C
for a detailed model of BPEL4WS LRTs based on WSTransaction concepts.
Additionally, it is important to
understand that the notion of LRT described here is purely local and occurs
within a single business process instance. There is no distributed coordination
regarding an agreed-upon outcome among multiple-participant services. The
achievement of distributed agreement is an orthogonal problem outside the scope
of BPEL4WS, to be solved by using the protocols described in the WS-Transaction
specification. The need to compose WS-transaction with BPEL4WS is recognized.
As an example of an LRT, consider
the planning and fulfillment of a travel itinerary. This can be viewed as an
LRT in which individual service reservations can use nested transactions within
the scope of the overall LRT. If the itinerary is cancelled, the reservation
transactions must be compensated for by cancellation transactions, and the
corresponding payment transactions must be compensated accordingly. For ACID
transactions in databases the transaction coordinator(s) and the resources that
they control know all of the uncommitted updates and the order in which they
must be reversed, and they are in full control of such reversal. In the case of
business transactions, the compensation behavior is itself a part of the
business logic and protocol, and must be explicitly specified. For example,
there might be penalties or fees applied for cancellation of an airline
reservation depending on the class of ticket and the timing. If a payroll
advance has been given to pay for the travel, the reservation must be
successfully cancelled before the payroll advance for it can be reversed in the
form of a payroll deduction. This means the compensation actions might need to
run in the same order as the original transactions, which is not the standard
or default in most transaction systems. Using activity scopes as the definition
of logical units of work, the LRT feature of BPEL4WS addresses these
requirements.
Scopes can delineate a part of
the behavior that is meant to be reversible in an applicationdefined way by a
compensation handler. Scopes with compensation and fault handlers can be nested
without constraint to arbitrary depth.
A compensation handler in the
current version of BPEL4WS is simply a wrapper for a compensation activity as
shown below. It is recognized that in many scenarios the compensation handler
needs to receive data about the current state of the world and return data
regarding the results of the compensation.
<compensationHandler>?
activity
</compensationHandler>
As explained in Invoking
Web Service Operations, there is a special shortcut for the invoke
activity to inline a compensation handler rather than explicitly using an
immediately enclosing scope. For example:
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
<correlations>
<correlation set="PurchaseOrder" initiate="yes"
pattern="out"/>
</correlations>
<compensationHandler>
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="CancelPurchase"
inputVariable="getResponse"
outputVariable="getConfirmation">
<correlations>
<correlation set="PurchaseOrder" pattern="out"/>
</correlations>
</invoke>
</compensationHandler>
</invoke>
In this example, the original
invoke activity makes a purchase and in case that purchase needs to be
compensated, the compensationHandler
invokes a cancellation operation at the same port of the same partnerLink,
using the response to the purchase request as the input.
In standard syntax (without the
invoke shortcut) this example would be equivalently expressed as follows:
<scope>
<compensationHandler>
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="CancelPurchase"
inputVariable="getResponse"
outputVariable="getConfirmation">
<correlations>
<correlation set="PurchaseOrder" pattern="out"/>
</correlations>
</invoke>
</compensationHandler>
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
<correlations>
<correlation set="PurchaseOrder" initiate="yes"
pattern="out"/>
</correlations>
</invoke>
</scope>
Note that the variable getResponse can be reused later for other purposes
before compensation is invoked. But the compensation handler needs the specific
response to the invoke operation
that is being reversed. BPEL4WS semantics state that the compensation handler,
if invoked, will see a frozen snapshot of all variables, as they were when the
scope being compensated was completed. In other words, if the compensation
handler shown here is used, the contents of getResponse that it will see and use are exactly the
contents at the time of the completion of the invoke activity it compensates.
This also means that compensation handlers cannot update live data in the
variables that the business process is using. They live entirely in a snapshot
world. A compensation handler, once installed, can be thought of as a
completely self-contained action that is not affected by, and does not affect,
the global state of the business process instance. It can only affect external
entities.
It is not realistic to expect
compensation activities to always be oblivious to the current state of the
world. In fact, compensation both affects and is affected by the current state.
However, the shape of the world within which compensation is run is difficult
to anticipate. It is therefore necessary to allow the two-way interaction
between compensation activities and the live world to take place in a tightly
controlled manner. In the future, BPEL4WS will add input and output parameters
to compensation handlers for this purpose.
As stated in The
Lifecycle of a Process, if a compensation handler is specified for
the business process as a whole, a business process instance can be compensated
after
normal completion by
platform-specific means. This functionality is enabled by setting the enableInstanceCompensation attribute of the process to "yes".
The compensation handler can be
invoked by using the compensate activity, which names the scope for which the compensation is to be
performed, that is, the scope whose compensation handler is to be invoked. A
compensation handler for a scope is available for invocation only when the
scope completes normally. Invoking a compensation handler that has not been
installed is equivalent to the empty activity (it is a no-op)—this ensures that fault handlers do not
have to rely on state to determine which nested scopes have completed
successfully. The semantics of a process in which an installed compensation
handler is invoked more than once is undefined.
Note that in case an invoke
activity has a compensation handler defined inline, the name of the activity is
the name of the scope to be used in the compensate activity.
<compensate scope="ncname"? standard-attributes>
standard-elements
</compensate>
The ability to explicitly invoke
the compensate activity is the underpinning of the
application-controlled error-handling framework of BPEL4WS. This activity can
be used only in the following parts of a business process:
·
In a
fault handler of the scope that immediately encloses the scope for which
compensation is to be performed.
·
In
the compensation handler of the scope that immediately encloses the scope for
which compensation is to be performed.
Example:
<compensate scope="RecordPayment"/>
If a scope being compensated by
name was nested in a loop, the instances of the compensation handlers in the
successive iterations are invoked in reverse order.
If the compensation handler for a
scope is absent, the default compensation handler invokes the compensation
handlers for the immediately enclosed scopes in the reverse order of the
completion of those scopes.
The <compensate/> form, in which the scope name is omitted
in a compensate activity, causes this default behavior to
be invoked explicitly. This is useful when an enclosing fault or compensation
handler needs to perform additional work, such as updating variables or sending
external notifications, in addition to performing default compensation for
inner scopes. Note that the <compensate/> activity in a fault or compensation handler
attached to scope S causes the default-order invocation of compensation
handlers for completed scopes directly nested within S. The use of this
activity can be mixed with any other user-specified behavior except the
explicit invocation of <compensate scope="Sx"/> for scope Sx nested directly within S.
Explicit invocation of compensation for such a scope nested within S disables
the availability of default-order compensation, as expected.
Fault handling in a business
process can be thought of as a mode switch from the normal processing in a
scope. Fault handling in BPEL4WS is always treated as "reverse work"
in that its sole aim is to undo the partial and unsuccessful work of a scope in
which a fault has occurred. The completion of the activity of a fault handler,
even when it does not rethrow the fault handled, is never considered successful
completion of the attached scope and compensation is never enabled for a scope
that has had an associated fault handler invoked.
The optional fault handlers
attached to a scope provide a way to define a set of custom fault-handling
activities, syntactically defined as catch activities. Each catch activity is defined to intercept a specific kind of fault, defined by a
globally unique fault QName and a variable for the data associated with the
fault. If the fault name is missing, then the catch will intercept all faults
with the right type of fault data. The fault variable is specified using the
faultVariable attribute in a catch handler. The variable is deemed to be
declared by virtue of being used as the value of this attribute and is local to
the fault handler. It is not visible or usable outside the fault handler in
which it is declared. The fault variable is optional because a fault might not
have additional data associated with it.
A fault response to an invoke
activity is one source of faults, with obvious name and data aspects based on
the definition of the fault in the WSDL operation. A programmatic throw activity is another source, again with
explicitly given name and data. The core concepts and exexutable pattern
extensions of BPEL4WS define several standard faults with their names and data,
and there might be other platform-specific faults such as communication
failures that can occur in a business process instance. A catchAll clause can be added to catch any fault
not caught by a more specific catch handler.
<faultHandlers>?
<!-- there must be at least one fault handler or default -->
<catch faultName="qname"? faultVariable="ncname"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
</faultHandlers>
Because of the flexibility
allowed in expressing the faults that a catch activity can handle, it is possible for a fault
to match more than one fault handler. The following rules are used to select
the catch activity that will process a fault:
·
If
the fault has no associated fault data, a catch activity that specifies a matching faultName value will be selected if present.
Otherwise, the default catchAll handler is selected if present.
·
If
the fault has associated fault data, a catch activity specifying a matching faultName value and
a faultVariable whose type (WSDL message type) matches
the type of the fault’s data will be selected if present. Otherwise, a
catch activity with no specified faultName and with a faultVariable whose type matches the type of the fault
data will be selected if present. Otherwise, the default catchAll handler is
selected if present.
If no catch or catchall is selected, the fault is not caught by the
current scope and is rethrown to the immediately enclosing scope (see Implicit Fault and Compensation Handlers for a more
complete description of the default fault and compensation handling behavior).
If the fault occurs in (or is rethrown to) the global process scope, and there
is no matching fault handler for the fault at the global level, the process
terminates abnormally, as though a terminate activity had been performed.
Consider the following example:
76
<faulthandlers>
<catch faultName="x:foo">
<empty/>
</catch>
<catch faultVariable="bar">
<empty/>
</catch>
<catch faultName="x:foo" faultVariable="bar">
<empty/>
</catch>
<catchAll>
<empty/>
</catchAll>
</faulthandlers>
Assume that a fault named
”x:foo” is thrown. The first catch will be selected if the fault carries no fault
data. If there is fault data associated with the fault, the third catch will be selected if and only if the type
of the fault’s data matches the type of variable “bar”,
otherwise the default catchall handler will be selected. Finally, a fault with a fault variable whose
type matches the type of “bar” and whose name is not
“x:foo” will be processed by the second catch. All other faults
will be processed by the default catchall handler.
Although the use of compensation
can be a key aspect of the behavior of fault handlers, each handler performs an
arbitrary activity, which can even be <empty/>. When a fault handler is present, it is
in charge of handling the fault. It might rethrow the same fault or a different
one, or it might handle the fault by performing cleanup and allowing normal
processing to continue in the enclosing scope.
A scope in which a fault occurred
is considered to have ended abnormally, whether or not the fault was caught and
handled without rethrow by a fault handler. A compensation handler is never
installed for a scope in which a fault occurred.
When a fault handler for scope S
handles a fault that occurred in S without rethrowing, links that have S as the
source will be subject to regular evaluation of status after the fault has been
handled, because processing in the enclosing scope is meant to be continued.
As explained in Invoking
Web Service Operations, there is a special shortcut for the invoke
activity to inline fault handlers rather than explicitly using an immediately
enclosing scope. For example:
<invoke partnerLink="Seller"
portType="SP:Purchasing"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
<catch faultName="SP:POFault" faultVariable="POFault">
<!-- handle the fault -->
</catch>
</invoke>
In this example, the original invoke makes a purchase and a fault handler is
inlined to handle the case where the purchase request results in a fault
response. In standard syntax (without the invoke shortcut), this example would be equivalently
expressed as follows:
<scope>
<faultHandlers>
<catch faultName="SP:POFault" faultVariable="POFault">
<!-- handle the fault -->
</catch>
</faultHandlers>
<invoke partnerLink="Seller"
portType="SP:Purchasing"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
</invoke>
</scope>
The compensation handler for
scope C becomes available for invocation by the fault and compensation handlers
for its immediately enclosing scope exactly when scope C completes normally. A
fault handler for scope C is available for invocation exactly when C has
commenced but has not been completed. If the scope faults before completion,
then the appropriate fault handler gets control and all other fault handlers
are uninstalled. It is never possible to run more than one fault handler for
the same scope under any circumstances.
Note that availability also
applies to Implicit Fault and Compensation Handlers.
The behavior of a fault handler
for scope C begins by implicitly terminating all activities that are currently
active and directly enclosed within C (see Semantics of
Activity Termination). The termination of these activities occurs
before the specific behavior of a fault handler is started. This also applies
to the implicit fault handlers described below. The activity of a fault handler
is deemed to occur in the scope to which the fault handler is attached.
Because the visibility of scope
names and therefore of compensation handlers is limited to the next enclosing
scope, the ability to compensate a scope would be lost if the enclosing scope
did not have a compensation handler or was missing a fault handler for some
fault. Because many faults are not programmatic or the result of operation
invocation, it is not reasonable to expect an explicit handler for every fault
in every scope. BPEL4WS therefore provides default compensation and fault
handlers when these are missing. The behavior of these implicit handlers is to
run available compensation handlers in the reverse order of completion of the
corresponding scopes. This is defined in more precise terms below.
Whenever a fault handler (for any
fault) or the compensation handler is missing for any given scope, they are
implicitly created with the following behavior:
Fault
handler:
·
Run
all available compensation handlers for immediately enclosed scopes in the
reverse order of completion of the corresponding scopes.
·
Rethrow
the fault to the next enclosing scope.
Compensation
handler:
·
Run
all available compensation handlers for immediately enclosed scopes in the
reverse order of completion of the corresponding scopes.
As stated above, the behavior of
a fault handler for scope C begins by implicitly terminating all activities
directly enclosed within C that are currently active. The following paragraphs
define what this means for all BPEL4WS activity types.
The assign activities are sufficiently short-lived that they
are allowed to complete rather than being interrupted when termination is
forced. The evaluation of expressions when already started is also allowed to
complete. Each wait, receive, reply and invoke activity is
interrupted and terminated prematurely. When a synchronous invoke activity (corresponding to a
request/reply operation) is interrupted and terminated prematurely, the
response (if received) for such a terminated activity is silently discarded.
The notion of termination does not apply to empty, terminate, and throw.
All structured activity behavior
is interrupted. The iteration of while is interrupted and termination is applied to the loop body activity. If switch has selected a branch, then the
termination is applied to the activity of the selected branch. The same applies
to pick. If either of these activities has not yet selected a branch, then the switch and the pick are terminated immediately. The sequence and flow constructs are terminated by terminating their
behavior and applying termination to all nested activities currently active
within them.
Scopes provide the ability to
control the semantics of forced termination to some degree. When the activity
being terminated is in fact a scope, the behavior of the scope is interrupted
and the fault handler for the standard bpws:forcedTermination fault is run. Note that this applies only
if the scope is in normal processing mode. If the scope has already experienced
an internal fault and invoked a fault handler, then as stated above, all other
fault handlers including the handler for bpws:forcedTermination are uninstalled, and the forced
termination has no effect. The already active fault handler is allowed to
complete.
The fault handler for the bpws:forcedTermination fault is designed like other fault
handlers, but this fault handler cannot rethrow any fault. Even if an uncaught
fault occurs during its behavior, it is not rethrown to the next enclosing
scope. This is because the enclosing scope has already faulted, which is what
is causing the forced termination of the nested scope.
In other respects this is a
normal fault handler. Its behavior begins by implicitly (recursively)
terminating all activities directly enclosed within its associated scope that
are currently active. It can invoke compensate activities. And when it is
missing, it is provided by using the same implicit behavior that is used for
all other implicit fault handlers.
Note that forced termination of
nested scopes occurs in innermost-first order as a result of the rule (quoted
above) that the behavior of any fault handler begins by implicitly
(recursively) terminating all activities directly enclosed within its
associated scope that are currently active.
Compensation handlers are always
invoked directly or indirectly as part of the processing of some fault handler
E. The behavior of a compensation handler invoked by E can cause a fault to be
thrown. Such a fault, if uncaught by scopes within the chain of compensation
handlers invoked by E, is treated as being a fault within E.
If a fault occurs in a fault
handler E for a scope C, the fault can be caught through the use of a scope within E. If the fault is not caught by a scope
within E, it is immediately thrown to the parent scope of C and the behavior of
E terminates prematurely. In effect, no distinction is made between faults that
E rethrows deliberately and faults that occur as undesired faults in E.
The whole process as well as each
scope can be associated with a set of event handlers that are invoked
concurrently if the corresponding event occurs. The actions taken within an
event handler can be any type of activity, such as sequence or flow, but
invocation of compensation handlers using the <compensate/> activity is
not permitted. As stated earlier, the <compensate/> activity can only be
used in fault and compensation handlers. There are two types of events. First,
events can be incoming messages that correspond to a request/response or
one-way operation in WSDL. For instance, a status query is likely to be a
request/response operation, whereas a cancellation may be a oneway operation.
Second, events can be alarms, that go off after user-set times. The grammar for
the set of event handlers associated with a scope or process is
<eventHandlers>?
<!-- there must be at least one onMessage or onAlarm handler -->
<onMessage partnerLink="ncname" portType="qname"
operation="ncname"
variable="ncname"?>*
<correlations>?
<correlation set="ncname" initiate="yes|no">+
</correlations>
activity
</onMessage>
<onAlarm for="duration-expr"? until="deadline-expr"?>*
activity
</onAlarm>
</eventHandlers>
It is important to emphasize that
event handlers are considered a part of the normal behavior of the scope,
unlike fault and compensation handlers.
The onMessage tag indicates that the event specified is an
event that waits for a message to arrive. The interpretation of this tag and
its attributes is very similar to a receive activity. The partnerLink attribute
defines the partner link on which the request is expected to arrive; the partnerLink must be defined in the partnerLinks section. The portType and operation
attributes define the appropriate port type and operation that is invoked by
the partner in order to cause the event. The variable attribute identifies the
variable which contains the message received from the partner. Note that the
operation may be either an asynchronous (oneway) or a synchronous
(request/response) operation. In the latter case the event handler is expected
to use a reply activity to send the response. The usage and interpretation of
correlation is exactly the same as for receive activities. It should also be
noted that an event cannot create a process instance.
The semantics of the onMessage
event is identical to a receive activity regarding the optional nature of the
variable attribute and the constraint regarding simultaneous enablement of
conflicting receive actions. For the latter, recall that the semantics of a process
in which two or more receive actions for the same partner link, portType, operation and correlation
set(s) may be simultaneously enabled is undefined (see Providing
Web Service Operations). Enablement of each onMessage event handler is equivalent to enablement
of the corresponding receive activity for the purposes of this constraint.
As specified in the grammar
above, event handlers for message events are not permitted to carry the
createInstance attribute. A business process instance cannot be created by a
message event. This is because the event handler cannot be enabled until the
instance is created.
When the message constituting an
event arrives, the activity specified in the corresponding handler is carried
out. The key point to understand is that the business process is enabled to
receive such messages concurrently with the normal activity of the scope to
which the event handler is attached. This allows such events to occur (or not
occur) at arbitrary times and an arbitrary number of times while the
corresponding scope (which may be the entire business process instance) is
active.
The following example shows the
usage of an event handler to support the termination of a process instance
through an external message. Alternatively, the event handler could throw a
fault to cause the ongoing work to be undone and compensated.
<process name=“orderCar”>
...
<eventHandlers>
<onMessage partnerLink=“buyer”
portType=“car”
operation=“cancel”
variable=“cancelDetails”>
<terminate/>
</onMessage>
...
</eventHandlers>
...
</process>
In this example, if the buyer
invokes the cancel operation on the port type car, the terminate activity is
carried out, which results in immediate termination of the process instance
without the ongoing work being undone and compensated. And this event is
attached to the global process scope and is therefore available during the
lifetime of the entire business process instance.
The onAlarm tag marks a timeout event. The for attribute
specifies the duration after which the event will be signaled. The clock for
the duration starts at the point in time when the associated scope starts. The
alternative until attribute specifies the specific point in time when the alarm
will be fired. Exactly one of these two attributes must occur in any onAlarm event.
The event handlers associated
with a scope are enabled when the associated scope starts .
If the event handler is
associated with the global process scope, the event handler is enabled as soon
as the process instance is created. The process instance is created when the
first receive activity that provides for the creation
of a process instance (indicated via the createInstance attribute set to "yes") has
received and processed the corresponding message. This allows the alarm time
for a global alarm event to be specified using the data provided within the
message that creates a process instance, as shown in the following example:
<wsdl:definitions
targetNamespace="http://www.example.com/wsdl/exmple"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
...>
<wsdl:message name=“orderDetails”>
<part name=“processDuration” type=“xsd:duration”/>
</wsdl:message>
</wsdl:definitions>
The message type above is used in
<process name=“orderCar”
xmlns:def="http://www.example.com/wsdl/example" ...>
...
<eventHandlers>
<onAlarm for=
“bpws:getVariableData(orderDetails,processDuration)” >
...
</onAlarm>
...
</eventHandlers>
...
<variable name=“orderDetails” messageType="def:orderDetails"/>
</variable>
...
<receive name=“getOrder”
partnerLink=“buyer”
portType=“car”
operation=“order”
variable=“orderDetails”
createInstance=“yes”/>
....
</process>
The onAlarm tag specifies a timer event that is fired when
the duration specified in the processDuration field in the orderDetails variable is exceeded. The value of the
field is provided via the getOrder activity that receives message containing the order details and causes the
creation of a process instance for that order.
The counting of time for an alarm
event with a duration starts when the enclosing event handler is activated. An
alarm event goes off when the specified time or duration has been reached. An
alarm event is carried out at most once while the corresponding scope is
active. The event is disabled for the rest of the activity of the corresponding
scope after it has occurred and the specified processing has been carried out.
A message event occurs when the
appropriate message is received on the specified partner link using the
specified port type and operation. When such an event occurs, the corresponding
activity is carried out. However, the event remains enabled, even for
concurrent use. Thus a particular message event can occur multiple times while
the corresponding scope is active. See below for concurrency considerations.
All event handlers associated
with a scope are disabled when the normal processing of the scope is complete.
The already dispatched event handlers are allowed to complete. The completion
of the scope as a whole is delayed until all active event handlers have
completed.
As we stated above, event
handlers are considered a part of the normal processing of the scope, i.e.,
active event handlers are concurrent activities within the scope. Faults within
event handlers are therefore faults within the associated scope. Moreover, if a
fault occurs within a scope, the behavior of the fault handler begins by
implicitly terminating all activities directly enclosed within the scope that
are currently active. This includes the activities within currently active
event handlers.
Multiple message and alarm events
can occur concurrently and they are treated as concurrent activities even if
they are request/response events representing the same partner link, port type,
operation and correlation sets. The constraint that there can be at most one
outstanding synchronous request on a given partner link at a given port type
and operation applies here as well (see Providing Web
Service Operations). Concurrent invocation of event handlers
necessarily relies heavily on the use of serializable scoping to ensure
consistent access to shared variables.
When the variableAccessSerializable attribute is set to "yes", the scope
provides concurrency control in governing access to shared variables. Such a
scope is called a serializable scope.
Serializable scopes must not be nested. A scope marked with variableAccessSerializable="yes" must be a leaf scope.
Suppose two concurrent
serializable scopes, S1 and S2, access a common set of variables (external to
them) for read or write operations. The semantics of serializability ensure
that the results of their behavior would be no different if all conflicting
activities (read/write and write/write activities) on any shared variable were
conceptually reordered in such a way that either all activities within S1 are
completed before those in S2 or vice versa. The actual mechanisms used to
ensure serializability are implementation dependent.
The use of error handling
features in a serializable scope is governed by the following rules:
·
The
fault handlers for a serializable scope share the serializability domain of the
associated scope, that is, in case a fault occurs in a serializable scope, the
behavior of the fault handler is considered part of the serializable behavior
(in commonly used implementation terms, locks are not released when making the
transition to the fault handler). This is because the repair of the fault needs
a shared isolation environment to provide predictable behavior.
·
The
compensation handler for a serializable scope does not share the
serializability domain of the associated scope.
·
For a
serializable scope with a compensation handler, the creation of the state snapshot
for compensation is part of the serializable behavior. In other words, it is
always possible to reorder behavior steps as if the scope had sufficiently
exclusive access to the shared variables all the way to completion, including
the creation of the snapshot.
It is useful to note that the
semantics of serializable scopes are very similar to the standard isolation
level "serializable" used in database transactions.
In this section we define the
essential extensions required for the use of BPEL4WS to define executable
processes. The extensions are grouped by the core concepts to which they apply.
These extensions refer to the Expressions feature of BPEL4WS.
The first extension defines a
standard fault for errorneous use of the XPath 1.0 function defined for
extracting global property values from variables.
bpws:getVariableProperty ('variableName', 'propertyName')
The first argument names the
source variable for the data and the second is the qualified name (QName) of
the global property to select from that variable (see Message
Properties). If the given property does not appear in any of the
parts of the variable's message type or the given property definition selects a
node set of a size other than one, then the standard fault bpws:selectionFailure MUST be thrown by a compliant
implementation.
The second extension defines an
additional XPath 1.0 function usable only in executable processes. This
function extracts arbitrary values from variables.
bpws:getVariableData ('variableName', 'partName'?, 'locationPath'?)
The first argument names the
source variable for the data, the second and third arguments are optional. When
present, the second names the part to select from that variable, and the third
optional argument, when present, provides an absolute location path (with '/'
meaning the root of the document fragment representing the entire part) to
identify the root of a subtree within the document fragment representing the
part.
When only the first argument is
present, the function extracts the value of the variable, which in this case
must be defined using an XML Schema simple type or element. Otherwise, the
return value of this function is a node set containing the single node
representing either an entire part of a message type(if the second argument is
present and the third argument is absent) or the result of the selection based
on the locationPath (if both optional arguments are present). If the given
locationPath selects a node set of a size other than one during execution, then
the standard fault bpws:selectionFailure MUST be thrown by a compliant implementation.
These extensions apply to the Variables feature of BPEL4WS.
An attempt during process
execution to use any part of a variable before it is initialized MUST result in
the standard bpws:uninitializedVariable fault.
These extensions apply to the Assignment feature of BPEL4WS.
The first extension adds an
additional assignment form.
In the first from-spec and to-spec variants of assignment, an optional query
attribute may be used in executable processes, yielding the forms
<from variable="ncname" part="ncname"? query="queryString"?/>
<to variable="ncname" part="ncname"? query="queryString"?/>
The value of the query attribute is a query string to identify a
single value within a source or target variable part. BPEL4WS provides an
extensible mechanism for the language used in these queries. The language is
specified by the attribute "queryLanguage" of the <process>
element. Compliant implementations of the current version of BPEL4WS MUST
support the use of XPath 1.0 as the query language. XPath 1.0 is indicated by
the default value of the queryLanguage attribute, which is:
http://www.w3.org/TR/1999/REC-xpath-19991116
For XPath 1.0, the value of the
query attribute MUST be an absolute locationPath (with '/' meaning the root of the document
fragment representing the entire part). It is used to identify the root of a
subtree within the document fragment representing the part. The location path
MUST select exactly one node. If the location path selects zero nodes or more
than one node during execution, then the standard fault bpws:selectionFailure MUST be thrown by a compliant
implementation.
The second extension defines a
standard fault for violation of type matching constraints. If any of the
matching constraints defined in the section Type
Compatibility in Assignment is violated during execution, the
standard fault bpws:mismatchedAssignmentFailure MUST be thrown by a compliant implementation.
The second extension defines the
behavior of assignment in the presence of failure during execution. An
important characteristic of assignment in BPEL4WS is that assignment activities
are atomic. If there is any fault during the
execution of an assignment activity, the destination variables are left
unchanged as they were at the start of the activity. This applies regardless of
the number of assignment elements within the overall assignment activity.
After a correlation set is initiated, the values of the
properties for a correlation set must be identical for all the messages in all
the operations that carry the correlation set and occur within the
corresponding scope until its completion. If at execution time this constraint
is violated, the standard fault bpws:correlationViolation MUST be thrown by a compliant implementation. The
same fault MUST be thrown if an activity with the initiate attribute set to no attempts to use a
correlation set that has not been previously initiated.
The first extension defines a
standard fault for the case where multiple conflicting receive activities
create ambiguity about message delivery.
If during the execution of a
business process instance, two or more receive activities for the same partner
link, portType, operation and correlation set(s) are in fact simultaneously
enabled, then the standard fault bpws:conflictingReceive MUST be thrown by a compliant implementation.
The second extension defines a
standard fault for the case where multiple outstanding synchronous requests
create an ambiguity about response correlation.
If more than one outstanding
synchronous request on a specific partner link for a particular portType,
operation and correlation set(s) is outstanding simultaneously during the
execution of a business process instance, then the standard fault bpws:conflictingRequest MUST be thrown by a compliant implementation.
Note that this is semantically different from the bpws:conflictingReceive, because it is possible to create the conflictingRequest by consecutively receiving the same
request on a specific partner link for a particular portType, operation and
correlation set(s). If a reply activity is being carried out during the execution of a business process
instance and no synchronous request is outstanding for the specified
partnerLink, portType, operation and correlation set(s), then the standard
fault bpws:invalidReply MUST be thrown by a compliant
implementation.
The third extension specifies
that the inputVariable attribute
for invoke and the variable attribute
for receive and replyactivities are not optional in executable
processes. In addition, the outputVariable attribute is not optional for invokewhen the operation concerned is a request/response operation.
The terminate activity can be used to immediately
terminate the behavior of a business process instance within which the terminate activity is performed. All currently
running activities MUST be terminated as soon as possible without any fault
handling or compensation behavior.
<terminate standard-attributes>
standard-elements
</terminate>If an installed compensation
handler is invoked more than once during the execution of a process instance, a
compliant implementation MUST throw the standard bpws:repeatedCompensation fault.
This extension explains the
relationship of onMessage event
handlers to the standard fault extension in Web Service
Operations for multiple conflicting receive activities create
ambiguity about message delivery Enablement of an onMessage event handler is equivalent to enablement
of a receive activity for the semantics of the occurrence of the bpws:conflictingReceiveFault fault (see Providing
Web Service Operations).
The inputVariable attribute for onMessage handlers is not optional in executable
processes. In addition, the outputVariable attribute is not optional for invoke when the operation concerned is a request/response operation.
There are two extensions for the
business protocol usage pattern.
This extension clarifies the
rules regarding variable initialization in abstract processes. Unlike
executable processes, variables in abstract processes do not need to be fully
initialized before being used since some computation is left implicit in abstract
processes. However, since message properties are meant to represent
"transparent," i.e., protocol relevant data, BPEL4WS requires that
all message properties in a message must be initialized before the message can
be used, for example before the variable of the message is used as the inputVariable in a Web Service operation invocation.
In many cases, the level of
abstraction appropriate in abstract processes makes it unnecessary to use
message variables in web service interaction activities, when the intent is to
simply constrain the sequencing of such activities, and the actual message data
is not relevant. To simplify these common cases it is permissible, in abstract
processes, to omit the variable reference attributes from the <invoke/>,
<receive/>, and <reply/> activities. The meaning of such an
omission must be stated clearly. If no variable is specified for an incoming
message, then the abstract process may not refer subsequently to the message or
its properties (if any). If the variable reference is omitted for an outgoing
message, then any properties of the message are considered to have been
initialized through opaque assignment, as described in the following section.
When variable references are
omitted, correlation set references may be interpreted as follows:
·
For
an incoming message which initializes a correlation set (initiator case), the
correlation set is deemed to be initialized.
·
For
an outgoing message which initializes a correlation set (initiator case), the
correlation tokens (which are message properties) are initialized through
implicit opaque assignment as described above.
·
For
an outgoing message which references but does not initialize a correlation set
(follower case), the proper initialization of the message properties is implicit.
In this case, the already initialized correlation set itself provides the token
values for the outgoing message.
Note that it is not possible to
mix the variable-using and variable-less web service interaction styles freely.
If a correlation set is initialized by rule 1 or 2 above, then outgoing
messages in the same correlated exchange must also refrain from referencing a
message variable. This restriction applies because it is not possible to
initialize the properties of the outgoing messages from the correlation set
alone.
This extension adds a special
form of assignment to abstract processes to permit the modeling of the
non-deterministic effects of private computation on external protocol behavior.
Abstract processes add a sixth from-spec variant to allow an opaque value to be
assigned based on non-deterministic choice, yielding the form:
<from opaque="yes">
The value of this form in the
interpretation of assignment is chosen nondeterministically from the XSD value
space of the target. It can only be used in assignments where the
"tospec" refers to a variable property. Two distinct use cases exist
for opaque assignment. If the value space of the target is suitably
constrained, then opaque assignment is a useful way to describe behavioral
alternatives where the mechanism for choosing the alternative is private or
otherwise external to the process specification. For this use case, the XSD
type of the target property must be one of the following:
·
xsd:boolean
·
A
type derived from xsd:string and
restricted by enumeration
·
A
type derived from any XSD integral numeric type restricted by either
enumeration or a combination of minExclusive or minInclusive and maxExclusive
or maxInclusive
A second use cases exists for
target properties which don’t meet these requirements. When the
target’s value space is not constrained, it is useful to think of opaque
assignment as providing a unique identifier. Semantically, each opaque
assignment of this form should be considered to generate a unique value similar
to a GUID. This style of opaque assignment is most useful to model the
initialization of properties used for correlation.
A process that uses assignment of
opaque values is clearly not executable in the normal sense. However, it is
feasible to emulate possible execution traces using assignment of random values
of the correct type.
This example presents the use of
a BPEL4WS abstract process to describe a rudimentary shipping service. This
service handles the shipment of orders. From the service point of view, orders
are composed of a number of items. The shipping service offers two types of
shipment: shipments where the items are held and shipped together and shipment
where the items are shipped piecemeal until all of the order is accounted for.
The context for the shipping
service is a two-party interaction between a customer and the service. This is
modeled in the following partnerLinkType definition:
<plnk:partnerLinkType name="shippingLT"
xmlns:plnk="http://schemas.xmlsoap.org/ws/2003/05/partner-link/">
<plnk:role name="shippingService">
<plnk:portType name="shippingServicePT"/>
</plnk:role>
<plnk:role name="shippingServiceCustomer">
<plnk:portType name="shippingServiceCustomerPT"/>
</plnk:role>
</plnk:partnerLinkType>
The corresponding message and
portType definitions are as follows:
<wsdl:definitions
targetNameSpace="http://ship.org/wsdl/shipping"
xmlns:ship= ...>
<message name="shippingRequestMsg">
<part name="shipOrder" type="ship:shipOrder"/>
</message>
<message name="shippingNoticeMsg">
<part name="shipNotice" type="ship:shipNotice"/>
</message>
<portType name="shippingServicePT">
<operation name="shippingRequest">
<input message="shippingRequestMsg"/>
</operation>
</portType>
<portType name="shippingServiceCustomerPT">
<operation name="shippingNotice">
<input message="shippingNoticeMsg"/>
</operation>
</portType>
</wsdl:definitions>The properties relevant to the
service behavior are:
·
The
ship order ID that is used to correlate the ship notice(s) with the ship order
(shipOrderID)
·
Whether
the order is to be shipped complete or not (shipComplete)
·
The
total number of items in the order (itemsTotal)
·
The
number of items referred to in a ship notice so that, when partial shipments
are acceptable, we can use this, along with itemsTotal, to track the overall fulfillment of the
shipment (itemsCount)
Here are the definitions for the
properties and their aliases:
<wsdl:definitions
targetNamespace="http://example.com/shipProps/"
xmlns:sns="http://ship.org/wsdl/shipping"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/">
<!-- types used in abstract processes are required to be finite domains.
The itemCountType is restricted by range -->
<wsdl:types>
<xsd:schema>
<xsd:simpleType name="itemCountType">
<xsd:restriction base="xsd:int">
<xsd:minInclusive value="1"/>
<xsd:maxInclusive value="50"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:schema>
</wsdl:types>
<bpws:property name="shipOrderID" type="xsd:int"/>
<bpws:property name="shipComplete" type="xsd:boolean"/>
<bpws:property name="itemsTotal" type="ship:itemCountType"/>
<bpws:property name="itemsCount" type="ship:itemCountType"/>
<bpws:property name="numItemsShipped" type="ship:itemCountType"/>
<bpws:propertyAlias propertyName="tns:shipOrderID"
messageType="sns:shippingRequestMsg"
part="shipOrder"
query="/ShipOrderRequestHeader/shipOrderID"/>
<bpws:propertyAlias propertyName="tns:shipOrderID"
messageType="sns:shippingNoticeMsg"
part="shipNotice"
query="/ShipNoticeHeader/shipOrderID"/>
<bpws:propertyAlias propertyName="tns:shipComplete"
messageType="sns:shippingRequestMsg"
part="shipOrder"
query="/ShipOrderRequestHeader/shipComplete"/>
<bpws:propertyAlias propertyName="tns:itemsTotal"
messageType="sns:shippingRequestMsg"
part="shipOrder"
query="/ShipOrderRequestHeader/itemsTotal"/>
<bpws:propertyAlias propertyName="tns:itemsCount"
messageType="sns:shippingNoticeMsg"
part="shipNotice"
query="/ShipNoticeHeader/itemsCount"/>
</wsdl:definitions>Next is the process definition.
For brevity, the abstract process definition does not include, for example, the
handling of error conditions (business or otherwise) that a complete
description would account for. The rough outline of the process is as follows:
receive shipOrder
switch
case shipComplete
send shipNotice
otherwise
itemsShipped := 0
while itemsShipped < itemsTotal
itemsCount := opaque // non-deterministic assignment
// corresponding e.g. to
// internal interaction with
// back-end system
send shipNotice
itemsShipped = itemsShipped + itemsCount
And here is the more complete
version:
<process name="shippingService"
targetNamespace="http://acme.com/shipping"
xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
xmlns:sns="http://ship.org/wsdl/shipping"
xmlns:props="http://example.com/shipProps/"
abstractProcess="yes">
<partnerLinks>
<partnerLink name="customer"
partnerLinkType="sns:shippingLT"
partnerRole="shippingServiceCustomer"
myRole="shippingService"/>
</partnerLinks>
<variables>
<variable name="shipRequest"
messageType="sns:shippingRequestMsg"/>
<variable name="shipNotice"
messageType="sns:shippingNoticeMsg"/>
<variable name="itemsShipped"
type="props:itemCountType"/>
</variables>
<correlationSets>
<correlationSet name="shipOrder"
properties="props:shipOrderID"/>
</correlationSets>
<sequence>
<receive partnerLink="customer"
portType="sns:shippingServicePT"
operation="shippingRequest"
variable="shipRequest">
<correlations>
<correlation set="shipOrder" initiate="yes"/>
</correlations>
</receive>
<switch>
<case condition=
"bpws:getVariableProperty('shipRequest','props:shipComplete')" >
<sequence>
<assign>
<copy>
<from variable="shipRequest" property="props:itemsCount"/>
<to variable="shipNotice" property="props:itemsCount"/>
</copy>
</assign>
<invoke partnerLink="customer"
portType="sns:shippingServiceCustomerPT"
operation="shippingNotice"
inputVariable="shipNotice">
<correlations>
<correlation set="shipOrder" pattern="out"/>
</correlations>
</invoke>
</sequence>
</case>
<otherwise>
<sequence>
<assign>
<copy>
<from expression="0"/>
<to variable="itemsShipped"/>
</copy>
</assign>
<while condition=
"bpws:getVariableData('itemsShipped') <
bpws:getVariableProperty('shipRequest','props:itemsTotal')">
<sequence>
<assign>
<copy>
<from opaque="yes"/>
<to variable="shipNotice" property="props:itemsCount"/>
</copy>
</assign>
<invoke partnerLink="customer"
portType="sns:shippingServiceCustomerPT"
operation="shippingNotice"
inputVariable="shipNotice">
<correlations>
<correlation set="shipOrder" pattern="out"/>
</correlations>
</invoke>
<assign>
<copy>
<from expression=
"bpws:getVariableData('itemsShipped')
+
bpws:getVariableProperty('shipNotice',
'props:itemsCount')"/>
<to variable="itemsShipped"/>
</copy>
</assign>
</sequence>
</while>
</sequence>
</otherwise>
</switch>
</sequence>
</process>This example considers a simple
loan approval Web Service that provides a port where customers can send their
requests for loans. Customers of the service send their loan requests,
including personal information and amount being requested. Using this
information, the loan service runs a simple process that results in either a
"loan approved" message or a "loan rejected" message. The
approval decision can be reached in two different ways, depending on the amount
requested and the risk associated with the requester. For low amounts (less
than $10,000) and low-risk individuals, approval is automatic. For high amounts
or medium and high-risk individuals, each credit request needs to be studied in
greater detail. Thus, to process each request, the loan service uses the
functionality provided by two other services. In the streamlined processing
available for lowamount loans, a "risk assessment" service is used to
obtain a quick evaluation of the risk associated with the requesting
individual. A full-fledged "loan approval" service (possibly
requiring direct involvement of a loan expert) is used to obtain in-depth
assessments of requests when the streamlined approval process does not apply.
The WSDL portType supported by
this service is shown below ("loanServicePT" portType). It is assumed
that an independent "loan.org" consortium has provided definitions of
the loan service portType as well as the risk assessment and in-depth loan
approval service, so all the required WSDL definitions appear in the same WSDL
document. In particular, the portTypes for the Web Services providing the risk
assessment and approval functions, and all the required partner link types that
relate to the use of these portTypes, are also defined there.
<definitions
targetNamespace="http://loans.org/wsdl/loan-approval"
xmlns="http://schemas.xmlsoap.org/wsdl/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:plnk="http://schemas.xmlsoap.org/ws/2003/05/partner-link/"
xmlns:lns="http://loans.org/wsdl/loan-approval">
<message name="creditInformationMessage">
<part name="firstName" type="xsd:string"/>
<part name="name" type="xsd:string"/>
<part name="amount" type="xsd:integer"/>
</message>
<message name="approvalMessage">
<part name="accept" type="xsd:string"/>
</message>
<message name="riskAssessmentMessage">
<part name="level" type="xsd:string"/>
</message>
<message name="errorMessage">
<part name="errorCode" type="xsd:integer"/>
</message>
<portType name="loanServicePT">
<operation name="request">
<input message="lns:creditInformationMessage"/>
<output message="lns:approvalMessage"/>
<fault name="unableToHandleRequest"
message="lns:errorMessage"/>
</operation>
</portType>
<portType name="riskAssessmentPT">
<operation name="check">
<input message="lns:creditInformationMessage"/>
<output message="lns:riskAssessmentMessage"/>
<fault name="loanProcessFault"
message="lns:errorMessage"/>
</operation>
</portType>
<portType name="loanApprovalPT">
<operation name="approve">
<input message="lns:creditInformationMessage"/>
<output message="lns:approvalMessage"/>
<fault name="loanProcessFault"
message="lns:errorMessage"/>
</operation>
</portType>
<plnk:partnerLinkType name="loanPartnerLinkType">
<plnk:role name="loanService">
<plnk:portType name="lns:loanServicePT"/>
</plnk:role>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="loanApprovalLinkType">
<plnk:role name="approver">
<plnk:portType name="lns:loanApprovalPT"/>
</plnk:role>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="riskAssessmentLinkType">
<plnk:role name="assessor">
<plnk:portType name="lns:riskAssessmentPT"/>
</plnk:role>
</plnk:partnerLinkType>
</definitions>In the business process defined
below, the interaction with the customer is represented by the initial
<receive> and the matching <reply> activities. The use of risk
assessment and loan approval services is represented by <invoke>
elements. All these activities are contained within a <flow>, and their
(potentially concurrent) behavior is staged according to the dependencies expressed
by corresponding <link> elements. Note that the transition conditions
attached to the <source> elements of the links determine which links get
activated. Dead path elimination is enabled by the value "yes" taken
by the "suppressJoinFailure" attribute on the <process>
element. This implies that as certain links are set false the consequences of
this decision can be propagated and the excecution of certain activities can be
skipped.
Because the operations invoked
can return a fault of type "loanProcessFault", a fault handler is
provided. When a fault occurs, control is transferred to the fault handler,
where a <reply> element is used to return a fault response of type
"unableToHandleRequest" to the loan requester.
<process name="loanApprovalProcess"
targetNamespace="http://acme.com/loanprocessing"
xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns:lns="http://loans.org/wsdl/loan-approval"
suppressJoinFailure="yes">
<partnerLinks>
<partnerLink name="customer"
partnerLinkType="lns:loanPartnerLinkType"
myRole="loanService"/>
<partnerLink name="approver"
partnerLinkType="lns:loanApprovalLinkType"
partnerRole="approver"/>
<partnerLink name="assessor"
partnerLinkType="lns:riskAssessmentLinkType"
partnerRole="assessor"/>
</partnerLinks>
<variables>
<variable name="request"
messageType="lns:creditInformationMessage"/>
<variable name="risk"
messageType="lns:riskAssessmentMessage"/>
<variable name="approval"
messageType="lns:approvalMessage"/>
<variable name="error"
messageType="lns:errorMessage"/>
</variables>
<faultHandlers>
<catch faultName="lns:loanProcessFault"
faultVariable="error">
<reply partnerLink="customer"
portType="lns:loanServicePT"
operation="request"
variable="error"
faultName="unableToHandleRequest"/>
</catch>
</faultHandlers>
<flow>
<links>
<link name="receive-to-assess"/>
<link name="receive-to-approval"/>
<link name="approval-to-reply"/>
<link name="assess-to-setMessage"/>
<link name="setMessage-to-reply"/>
<link name="assess-to-approval"/>
</links>
<receive partnerLink="customer"
portType="lns:loanServicePT"
operation="request"
variable="request" createInstance="yes">
<source linkName="receive-to-assess"
transitionCondition=
"bpws:getVariableData('request','amount')< 10000"/>
<source linkName="receive-to-approval"
transitionCondition=
"bpws:getVariableData('request','amount')>=10000"/>
</receive>
<invoke partnerLink="assessor"
portType="lns:riskAssessmentPT"
operation="check"
inputVariable="request"
outputVariable="risk">
<target linkName="receive-to-assess"/>
<source linkName="assess-to-setMessage"
transitionCondition=
"bpws:getVariableData('risk','level')='low'"/>
<source linkName="assess-to-approval"
transitionCondition=
"bpws:getVariableData('risk','level')!='low'"/>
</invoke>
<assign>
<target linkName="assess-to-setMessage"/>
<source linkName="setMessage-to-reply"/>
<copy>
<from expression="'yes'"/>
<to variable="approval" part="accept"/>
</copy>
</assign>
<invoke partnerLink="approver"
portType="lns:loanApprovalPT"
operation="approve"
inputVariable="request"
outputVariable="approval">
<target linkName="receive-to-approval"/>
<target linkName="assess-to-approval"/>
<source linkName="approval-to-reply" />
</invoke>
<reply partnerLink="customer"
portType="lns:loanServicePT"
operation="request"
variable="approval">
<target linkName="setMessage-to-reply"/>
<target linkName="approval-to-reply"/>
</reply>
</flow>
</process>A process can have multiple
activities that create a process instance. An example of this situation is a
(simplified) business process run by an auction house. The purpose of the
business process is to collect information from the buyer and the seller of a
particular auction, report the appropriate auction results to some auction
registration service, and then send the registration result back to the seller
and the buyer. Thus the business process starts with two activities, one for
receiving the seller information and one for receiving the buyer information.
Because a particular auction is uniquely identified by an auction ID, the
seller and the buyer need to provide this information when sending in their
data. The sequence in which the seller and buyer requests arrive at the auction
house is random. Thus, when such a request comes in, it needs to be checked
whether a business process instance exists already or not. If not, a business
process instance is created. After both requests have been received, the
auction registration service is invoked. Because the invocation is done
asynchronously, the auction house passes the auction ID to the auction
registration service. The auction registration service returns this auction ID
in its answer so that the auction house can locate the proper business process
instance. Because there are many buyers and sellers, each of them needs to
provide their endpoint references, so that the auction service can respond
properly. In addition, the auction house needs to provide its own endpoint
reference to the auction registration service so that the auction registration
service can send the response back to the auction house.
The auction service offers two
port types, called sellerPT and buyerPT, with appropriate operations for
accepting the data provided by the seller and the buyer. Because the processing
time of the business process is lengthy, the auction service responds to the
seller and buyer through appropriate port types, sellerAnswerPT and
buyerAnswerPT. These portTypes are properly combined into two partner link
types, one for the seller called sellerAuctionHouseLT and one for the buyer
called buyerAuctionHouseLT.
The auction service needs two
port types, called auctionRegistrationPT and auctionRegistrationAnswerPT, that
provide for the invocation of the auction registration service. The port types
are part of the appropriate partner link type
auctionHouseAuctionRegistrationServiceLT.
<definitions
targetNamespace="http://www.auction.com/wsdl/auctionService"
xmlns:tns="http://www.auction.com/wsdl/auctionService"
xmlns:plnk="http://schemas.xmlsoap.org/ws/2003/05/partner-link/"
xmlns:wsa="http://schemas.xmlsoap.org/ws/2003/03/addressing"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- Messages for communication with the seller -->
<message name="sellerData">
<part name="creditCardNumber" type="xsd:string"/>
<part name="shippingCosts" type="xsd:integer"/>
<part name="auctionId" type="xsd:integer"/>
<part name="endpointReference" type="wsa:EndpointReferenceType"/>
</message>
<message name="sellerAnswerData">
<part name="thankYouText" type="xsd:string"/>
</message>
<!-- Messages for communication with the buyer -->
<message name="buyerData">
<part name="creditCardNumber" type="xsd:string"/>
<part name="phoneNumber" type="xsd:string"/>
<part name="ID" type="xsd:integer"/>
<part name="endpointReference" type="wsa:EndpointReferenceType"/>
</message>
<message name="buyerAnswerData">
<part name="thankYouText" type="xsd:string"/>
</message>
<!-- Messages for communication with the auction registration service -->
<message name="auctionData">
<part name="auctionId" type="xsd:integer"/>
<part name="amount" type="xsd:integer"/>
</message>
<message name="auctionAnswerData">
<part name="registrationId" type="xsd:integer"/>
<part name="auctionId" type="xsd:integer"/>
<part name="auctionHouseEndpointReference"
type="wsa:EndpointReferenceType"/>
</message>
<!-- Port types for interacting with the seller -->
<portType name="sellerPT">
<operation name="submit">
<input message="tns:sellerData"/>
</operation>
</portType>
<portType name="sellerAnswerPT">
<operation name="answer">
<input message="tns:sellerAnswerData"/>
</operation>
</portType>
<!-- Port types for interacting with the buyer -->
<portType name="buyerPT">
<operation name="submit">
<input message="tns:buyerData"/>
</operation>
</portType>
<portType name="buyerAnswerPT">
<operation name="answer">
<input message="tns:buyerAnswerData"/>
</operation>
</portType>
<!-- Port types for interacting with the auction registration service -->
<portType name="auctionRegistrationPT">
<operation name="process">
<input message="tns:auctionData"/>
</operation>
</portType>
<portType name="auctionRegistrationAnswerPT">
<operation name="answer">
<input message="tns:auctionAnswerData"/>
</operation>
</portType>
<!-- Context type used for locating business process via auction Id -->
<bpws:property name="auctionId"
type="xsd:string"/>
<bpws:propertyAlias propertyName="tns:auctionId"
messageType="tns:sellerData"
part="auctionId"/>
<bpws:propertyAlias propertyName="tns:auctionId"
messageType="tns:buyerData"
part="ID"/>
<bpws:propertyAlias propertyName="tns:auctionId"
messageType="tns:auctionData"
part="auctionId"/>
<bpws:propertyAlias propertyName="tns:auctionId"
messageType="tns:auctionAnswerData"
part="auctionId"/>
<!-- Partner link type for seller/auctionHouse -->
<plnk:partnerLinkType name="tns:sellerAuctionHouseLT">
<plnk:role name="auctionHouse">
<plnk:portType name="tns:sellerPT"/>
</plnk:role>
<plnk:role name="seller">
<plnk:portType name="tns:sellerAnswerPT"/>
</plnk:role>
</plnk:partnerLinkType>
<!-- Partner link type for buyer/auctionHouse -->
<plnk:partnerLinkType name="buyerAuctionHouseLT">
<plnk:role name="auctionHouse">
<plnk:portType name="tns:buyerPT"/>
</plnk:role>
<plnk:role name="buyer">
<plnk:portType name="tns:buyerAnswerPT"/>
</plnk:role>
</plnk:partnerLinkType>
<!-- Partner link type for auction house/auction
registration service -->
<plnk:partnerLinkType name="auctionHouseAuctionRegistrationServiceLT">
<plnk:role name="auctionRegistrationService">
<plnk:portType name="tns:auctionRegistrationPT"/>
</plnk:role>
<plnk:role name="auctionHouse">
<plnk:portType name="tns:auctionRegistrationAnswerPT"/>
</plnk:role>
</plnk:partnerLinkType>
</definitions>The BPEL4WS definition for the
business process offered by the auction house follows:
<process name="auctionService"
targetNamespace="http://www.auction.com"
variableAccessSerializable="no"
xmlns:as="http://www.auction.com/wsdl/auctionService"
xmlns:wsa="http://schemas.xmlsoap.org/ws/2003/03/addressing"
xmlns="http://schemas.xmlsoap.org/ws/2003/03/business-process/">
<!-- Partners -->
<partnerLinks>
<partnerLink name="seller"
partnerLinkType="as:sellerAuctionHouseLT"
myRole="auctionHouse" partnerRole="seller"/>
<partnerLink name="buyer"
partnerLinkType="as:buyerAuctionHouseLT"
myRole="auctionHouse" partnerRole="buyer"/>
<partnerLink name="auctionRegistrationService"
partnerLinkType=
"as:auctionHouseAuctionRegistrationServiceLT"
myRole="auctionHouse"
partnerRole="auctionRegistrationService"/>
</partnerLinks>
<!-- Variables -->
<variables>
<variable name="sellerData" messageType="as:sellerData"/>
<variable name="sellerAnswerData" messageType="as:sellerAnswerData"/>
<variable name="buyerData" messageType="as:buyerData"/>
<variable name="buyerAnswerData" messageType="as:buyerAnswerData"/>
<variable name="auctionData"
messageType="as:auctionData"/>
<variable name="auctionAnswerData"
messageType="as:auctionAnswerData"/>
</variables>
<!-- Correlation set for correlating buyer and seller request
as well as auction house and auction registration service exchange -->
<correlationSets>
<correlationSet name="auctionIdentification"
properties="as:auctionId"/>
</correlationSets>
<!-- Structure of the business process -->
<sequence>
<!-- Process buyer and seller request concurrently
Either one can create a process instance -->
<flow>
<!-- Process seller request -->
<receive name="acceptSellerInformation"
partnerLink="seller"
portType="as:sellerPT"
operation="provide"
variable="sellerData"
createInstance="yes">
<correlations>
<correlation set="auctionIdentification"
initiate="yes"/>
</correlations>
</receive>
<!-- Process buyer request -->
<receive name="acceptBuyerInformation"
partnerLink="buyer"
portType="as:buyerPT"
operation="provide"
variable="buyerData"
createInstance="yes">
<correlations>
<correlation set="auctionIdentification"
initiate="yes"/>
</correlations>
</receive>
</flow>
<!-- Invoke auction registration service by setting the target endpoint
reference and setting my own endpoint reference for call back
and receiving the answer Correlation of request and answer is
via auction Id -->
<assign>
<copy>
<from>
<wsa:EndpointReference>
<wsa:Address>xs:anyURI</wsa:Address>
<wsa:ServiceName>ars:RegistrationService</wsa:ServiceName>
</wsa:EndpointReference>
</from>
<to partnerLink="auctionRegistrationService"/>
</copy>
</assign>
<assign>
<copy>
<from partnerLink="auctionRegistrationService"
endpointReference="myRole"/>
<to variable="auctionData"
part="auctionHouseServiceRef"/>
</copy>
</assign>
<invoke name="registerAuctionResults"
partnerLink="auctionRegistrationService"
portType="as:auctionRegistrationPT"
operation="process"
inputVariable="auctionData">
<correlations>
<correlation set="auctionIdentification"/>
</correlations>
</invoke>
<receive name="receiveAuctionRegistrationInformation"
partnerLink="auctionRegistrationService"
portType="as:auctionRegistrationAnswerPT"
operation="answer"
variable="auctionAnswerData">
<correlations>
<correlation set="auctionIdentification"/>
</correlations>
</receive>
<!-- Send responses back to seller and buyer -->
<flow>
<!-- Process seller response by setting the seller to
the endpoint reference provided by the seller
and invoking the response -->
<sequence>
<assign>
<copy>
<from variable="sellerData"
part="endpointReference"/>
<to partnerLink="seller"/>
</copy>
</assign>
<invoke name="respondToSeller"
partnerLink="seller"
portType="as:sellerAnswerPT"
operation="answer"
inputVariable="sellerAnswerData"/>
</sequence>
<!-- Process buyer response by setting the buyer to
the endpoint reference provided by the buyer
and invoking the response -->
<sequence>
<assign>
<copy>
<from variable="buyerData"
part="endpointReference"/>
<to partnerLink="buyer"/>
</copy>
</assign>
<invoke name="respondToBuyer"
partnerLink="buyer"
portType="as:buyerAnswerPT"
operation="answer"
inputVariable="buyerAnswerData"/>
</sequence>
</flow>
</sequence>
</process>Because messages can be modified
or forged, it is strongly RECOMMENDED that business process implementations use
WS-Security to ensure messages have not been modified or forged while in
transit or while residing at destinations. Similarly, invalid or expired
messages could be re-used or message headers not specifically associated with
the specific message could be referenced. Consequently, when using WS-Security,
signatures MUST include the semantically significant headers and the message
body (as well as any other relevant data) so that they cannot be independently
separated and re-used.
Messaging protocols used to
communicate among business processes are subject to various forms of replay
attacks. In addition to the mechanisms listed above, messages SHOULD include a
message timestamp (as described in WS-Security) within the signature.
Recipients can use the timestamp information to cache the most recent messages
for a business process and detect duplicate transmissions and prevent potential
replay attacks.
It should also be noted that
business process implementations are subject to various forms of
denial-of-service attacks. Implementers of business process execution systems
compliant with this specification should take this into account.
A. Standard
Faults
The following list specifies the
standard faults defined within the BPEL4WS specification. All these faults are
named within the BPEL4WS namespace standard prefix bpws: corresponding to URI
"http://schemas.xmlsoap.org/ws/2003/03/business-process/".
|
Fault name |
Reason |
|
selectionFailure |
Thrown when a selection operation performed either in a function such as bpws:getVariableData, or in an assignment, encounters an error. |
|
conflictingReceive |
Thrown when more than one receive activity or equivalent (currently, onMessage branch in a pick activity) are enabled simultaneously for the same partner link, port type, operation and correlation set(s). |
|
conflictingRequest |
Thrown when more than one synchronous inbound request on the same partner link for a particular port type, operation and correlation set(s) are active. |
|
mismatchedAssignmentFailure |
Thrown when incompatible types are encountered in an assign activity. |
|
joinFailure |
Thrown when the join condition of an activity evaluates to false. |
|
forcedTermination |
Thrown as the result of a fault in an enclosing scope. |
|
correlationViolation |
Thrown when the contents of the messages that are processed in an invoke, receive, or reply activity do not match specified correlation information. |
|
uninitializedVariable |
Thrown when there is an attempt to access the value of an uninitialized part in a message variable. |
|
repeatedCompensation |
Thrown when an installed compensation handler is invoked more than once. |
|
invalidReply |
Thrown when a reply is sent on a partner link, portType and operation for which the corresponding receive with the same correlation has not been carried out. |
B. Attributes
and Defaults
The following list specifies the
defaults for all standard attributes at the process and activity level. The
table does not include activity-specific attributes (such as partnerLink in an invoke activity).
Table B.1. Attributes and Defaults
|
Parameter |
Default |
|
queryLanguage |
http://www.w3.org/TR/1999/REC-xpath-19991116 |
|
expressionLanguage |
http://www.w3.org/TR/1999/REC-xpath-19991116 |
|
suppressJoinFailure |
no |
|
variableAccessSerializable |
no |
|
abstractProcess |
no |
|
initiate |
no |
|
pattern |
No default |
|
createInstance |
no |
|
enableInstanceCompensation |
no |
|
joinCondition |
Disjunction of the status of the incoming links |
|
transitionCondition |
true |
C. Coordination
Protocol
It is valuable to express the
fault and compensation handling relationship between scopes by using the
protocol framework of [WS-Transaction].
Specifically, this section shows how the relationship between an enclosing scope
and each of its nested scopes can be modeled using the BusinessAgreement
protocol defined in the WS-Transaction specification. The BusinessAgreement
protocol is designed to enable distributed coordination of business activities.
BPEL4WS usage of the protocol makes the assumption of localized behavior in a
single service, and as a result several of the features of the protocol,
including the acknowledgement signal Forget, and the Error and Replay messages, are not actually needed in BPEL4WS.
Coordination
Protocol for BPEL4WS Scopes
·
A
nested scope may complete successfully. In this case a compensation handler is
installed for the nested scope. This is modeled with a Completed signal from the nested scope to its
parent scope.
·
A
nested scope may encounter a fault internally. In this case the scope always
terminates unsuccessfully.
o If the fault handler rethrows a fault to
its enclosing scope, this is modeled as a Faulted signal from the nested scope to its parent scope.
o If the fault is handled and not rethrown,
the scope exits gracefully from the work of its parent scope. This is modeled
as an Exited signal from the nested scope to its
parent scope.
·
After
a nested scope has completed, (a fault or compensation handler for) the parent
scope may ask it to compensate itself by invoking its compensation handler. The
compensate action is modeled with a Compensate signal from the parent scope to the nested scope.
·
Upon
successful completion of the compensation, the nested scope sends the Compensated signal to its parent scope.
·
The
compensation handler may itself fault internally. In this case
o If the fault is not handled by a scope
within the compensation handler, it is rethrown to the parent scope. This is
modeled as a Faulted signal from
the nested scope to its parent scope.
o If the fault is handled and not rethrown,
we assume that the compensation was able to complete successfully. In this case
the nested scope sends the Compensated signal to its parent scope.
·
If
there is a fault in the parent scope independent of the work of the nested
scope, the parent scope will ask the nested scope to prematurely abandon its
work by sending a Cancel signal.
·
The
nested scope, upon receiving the cancel signal, will interrupt and terminate
its behavior (as though there were an internal fault), and return a Canceled signal to the parent.
·
Finally,
when a parent scope decides that the compensation for a completed nested scope
is not needed any more it sends a Close signal to the nested scope. After discarding the compensation handler the
nested scope responds with a Closed signal.
·
In
case there is a race between the Completed signal from the nested scope and the Cancel signal from the parent scope, the Completed signal wins, i.e., the nested scope is
deemed to have completed and the Cancel signal is ignored.
·
In
case a Cancelsignal is sent to a nested scope that has
already faulted internally, the Cancel signal is ignored and the scope will eventually send either a Faulted or an Exited signal to the parent.
The BusinessAgreement protocol
state diagram above summarizes the preceding discussion. In the diagram, the
parent (enclosing) scope generates Cancel, Compensate, Forget and Close signals and the nested scope generates Completed, Faulted,
Exited, Compensated, Canceled and Closed signals. It
is important to emphasize that the states represent the state of the
relationship between the parent scope and one specific nested scope. However,
it is very nearly the case that the states represent the state of the nested
scope itself, except in case of signal races. Note that the signal races
discussed in points I and J above are not reflected in the diagram since the
diagram only reflects real protocol states.
D. XSD
Schemas
BPEL4WS
Schema
<?xml version='1.0' encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"
xmlns:bpws="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
targetNamespace="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
elementFormDefault="qualified">
<import namespace="http://schemas.xmlsoap.org/wsdl/"
schemaLocation="http://schemas.xmlsoap.org/wsdl/"/>
<complexType name="tExtensibleElements">
<annotation>
<documentation>
This type is extended by other component types
to allow elements and attributes from
other namespaces to be added.
</documentation>
</annotation>
<sequence>
<any namespace="##other" minOccurs="0" maxOccurs="unbounded"
processContents="lax"/>
</sequence>
<anyAttribute namespace="##other" processContents="lax"/>
</complexType>
<element name="process" type="bpws:tProcess"/>
<complexType name="tProcess">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="partnerLinks" type="bpws:tPartnerLinks" minOccurs="0"/>
<element name="partners" type="bpws:tPartners" minOccurs="0"/>
<element name="variables" type="bpws:tVariables" minOccurs="0"/>
<element name="correlationSets" type="bpws:tCorrelationSets" minOccurs="0"/>
<element name="faultHandlers" type="bpws:tFaultHandlers" minOccurs="0"/>
<element name="compensationHandler" type="bpws:tCompensationHandler" minOccurs="0"/>
<element name="eventHandlers" type="bpws:tEventHandlers" minOccurs="0"/>
<group ref="bpws:activity"/>
</sequence>
<attribute name="name" type="NCName" use="required"/>
<attribute name="targetNamespace" type="anyURI" use="required"/>
<attribute name="queryLanguage" type="anyURI"
default="http://www.w3.org/TR/1999/REC-xpath-19991116"/>
<attribute name="expressionLanguage" type="anyURI"
default="http://www.w3.org/TR/1999/REC-xpath-19991116"/>
<attribute name="suppressJoinFailure" type="bpws:tBoolean"
default="no"/>
<attribute name="enableInstanceCompensation"
type="bpws:tBoolean" default="no"/>
<attribute name="abstractProcess" type="bpws:tBoolean" default="no"/>
</extension>
</complexContent>
</complexType>
<group name="activity">
<choice>
<element name="empty" type="bpws:tEmpty"/>
<element name="invoke" type="bpws:tInvoke"/>
<element name="receive" type="bpws:tReceive"/>
<element name="reply" type="bpws:tReply"/>
<element name="assign" type="bpws:tAssign"/>
<element name="wait" type="bpws:tWait"/>
<element name="throw" type="bpws:tThrow"/>
<element name="terminate" type="bpws:tTerminate"/>
<element name="flow" type="bpws:tFlow"/>
<element name="switch" type="bpws:tSwitch"/>
<element name="while" type="bpws:tWhile"/>
<element name="sequence" type="bpws:tSequence"/>
<element name="pick" type="bpws:tPick"/>
<element name="scope" type="bpws:tScope"/>
</choice>
</group>
<complexType name="tPartnerLinks">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="partnerLink" type="bpws:tPartnerLink"
minOccurs="1" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tPartnerLink">
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="name" type="NCName" use="required"/>
<attribute name="partnerLinkType" type="QName"
use="required"/>
<attribute name="myRole" type="NCName"/>
<attribute name="partnerRole" type="NCName"/>
</extension>
</complexContent>
</complexType>
<complexType name="tPartners">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="partner" type="bpws:tPartner"
minOccurs="1" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tPartner">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="partnerLink" minOccurs="1"
maxOccurs="unbounded">
<complexType>
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="name" type="NCName" use="required"/>
</extension>
</complexContent>
</complexType>
</element>
</sequence>
<attribute name="name" type="NCName" use="required"/>
</extension>
</complexContent>
</complexType>
<complexType name="tFaultHandlers">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="catch" type="bpws:tCatch"
minOccurs="0" maxOccurs="unbounded"/>
<element name="catchAll"
type="bpws:tActivityOrCompensateContainer"
minOccurs="0"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tCatch">
<complexContent>
<extension base="bpws:tActivityOrCompensateContainer">
<attribute name="faultName" type="QName"/>
<attribute name="faultVariable" type="NCName"/>
</extension>
</complexContent>
</complexType>
<complexType name="tActivityContainer">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<group ref="bpws:activity"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tActivityOrCompensateContainer">
<complexContent>
<extension base="bpws:tExtensibleElements">
<choice>
<group ref="bpws:activity"/>
<element name="compensate" type="bpws:tCompensate"/>
</choice>
</extension>
</complexContent>
</complexType>
<complexType name="tEventHandlers">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="onMessage" type="bpws:tOnMessage"
minOccurs="0" maxOccurs="unbounded"/>
<element name="onAlarm" type="bpws:tOnAlarm"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tOnMessage">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="correlations" type="bpws:tCorrelations"
minOccurs="0"/>
<group ref="bpws:activity"/>
</sequence>
<attribute name="partnerLink" type="NCName" use="required"/>
<attribute name="portType" type="QName" use="required"/>
<attribute name="operation" type="NCName" use="required"/>
<attribute name="variable" type="NCName" use="optional"/>
</extension>
</complexContent>
</complexType>
<complexType name="tOnAlarm">
<complexContent>
<extension base="bpws:tActivityContainer">
<attribute name="for" type="bpws:tDuration-expr"/>
<attribute name="until" type="bpws:tDeadline-expr"/>
</extension>
</complexContent>
</complexType>
<complexType name="tCompensationHandler">
<complexContent>
<extension base="bpws:tActivityOrCompensateContainer"/>
</complexContent>
</complexType>
<complexType name="tVariables">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="variable"
type="bpws:tVariable"
maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tVariable">
<!-- variable does not allow extensibility elements
because otherwise its content model would be non-deterministic -->
<attribute name="name" type="NCName" use="required"/>
<attribute name="messageType" type="QName" use = “optional”/>
<attribute name="type" type="QName" use = “optional”/>
<attribute name="element" type="QName" use = “optional”/>
<anyAttribute namespace="##other" processContents="lax"/>
</complexType>
<complexType name="tCorrelationSets">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="correlationSet"
type="bpws:tCorrelationSet"
maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tCorrelationSet">
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="properties" use="required">
<simpleType>
<list itemType="QName"/>
</simpleType>
</attribute>
<attribute name="name" type="NCName" use="required"/>
</extension>
</complexContent>
</complexType>
<complexType name="tActivity">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="target" type="bpws:tTarget"
minOccurs="0" maxOccurs="unbounded"/>
<element name="source" type="bpws:tSource"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
<attribute name="name" type="NCName"/>
<attribute name="joinCondition"
type="bpws:tBoolean-expr"/>
<attribute name="suppressJoinFailure"
type="bpws:tBoolean" default="no"/>
</extension>
</complexContent>
</complexType>
<complexType name="tSource">
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="linkName" type="NCName" use="required"/>
<attribute name="transitionCondition"
type="bpws:tBoolean-expr"/>
</extension>
</complexContent>
</complexType>
<complexType name="tTarget">
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="linkName" type="NCName" use="required"/>
</extension>
</complexContent>
</complexType>
<complexType name="tEmpty">
<complexContent>
<extension base="bpws:tActivity"/>
</complexContent>
</complexType>
<complexType name="tCorrelations">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="correlation" type="bpws:tCorrelation"
minOccurs="1" maxOccurs="unbounded" />
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tCorrelation">
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="set" type="NCName" use="required"/>
<attribute name="initiate" type="bpws:tBoolean" default="no"/>
</extension>
</complexContent>
</complexType>
<complexType name="tCorrelationsWithPattern">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="correlation"
type="bpws:tCorrelationWithPattern"
minOccurs="1"
maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tCorrelationWithPattern">
<complexContent>
<extension base="bpws:tCorrelation">
<attribute name="pattern">
<simpleType>
<restriction base="string">
<enumeration value="in" />
<enumeration value="out" />
<enumeration value="out-in" />
</restriction>
</simpleType>
</attribute>
</extension>
</complexContent>
</complexType>
<complexType name="tInvoke">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="correlations"
type="bpws:tCorrelationsWithPattern"
minOccurs="0" maxOccurs="1"/>
<element name="catch" type="bpws:tCatch"
minOccurs="0" maxOccurs="unbounded"/>
<element name="catchAll"
type="bpws:tActivityOrCompensateContainer"
minOccurs="0"/>
<element name="compensationHandler"
type="bpws:tCompensationHandler" minOccurs="0"/>
</sequence>
<attribute name="partnerLink" type="NCName" use="required"/>
<attribute name="portType" type="QName" use="required"/>
<attribute name="operation" type="NCName" use="required"/>
<attribute name="inputVariable" type="NCName" use="optional"/>
<attribute name="outputVariable" type="NCName" use="optional"/>
</extension>
</complexContent>
</complexType>
<complexType name="tReceive">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="correlations"
type="bpws:tCorrelations" minOccurs="0"/>
</sequence>
<attribute name="partnerLink" type="NCName" use="required"/>
<attribute name="portType" type="QName" use="required"/>
<attribute name="operation" type="NCName" use="required"/>
<attribute name="variable" type="NCName" use="optional"/>
<attribute name="createInstance" type="bpws:tBoolean" default="no"/>
</extension>
</complexContent>
</complexType>
<complexType name="tReply">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="correlations"
type="bpws:tCorrelations" minOccurs="0"/>
</sequence>
<attribute name="partnerLink" type="NCName" use="required"/>
<attribute name="portType" type="QName" use="required"/>
<attribute name="operation" type="NCName" use="required"/>
<attribute name="variable" type="NCName" use="optional"/>
<attribute name="faultName" type="QName"/>
</extension>
</complexContent>
</complexType>
<complexType name="tAssign">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="copy" type="bpws:tCopy"
minOccurs="1" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tCopy">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element ref="bpws:from"/>
<element ref="bpws:to"/>
</sequence>
</extension>
</complexContent>
</complexType>
<element name="from" type="bpws:tFrom"/>
<complexType name="tFrom">
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="variable" type="NCName"/>
<attribute name="part" type="NCName"/>
<attribute name="query" type="string"/>
<attribute name="property" type="QName"/>
<attribute name="partnerLink" type="NCName"/>
<attribute name="endpointReference" type="bpws:tRoles"/>
<attribute name="expression" type="string"/>
<attribute name="opaque" type="bpws:tBoolean"/>
</extension>
</complexContent>
</complexType>
<element name="to">
<complexType>
<complexContent>
<restriction base="bpws:tFrom">
<attribute name="expression" type="string"
use="prohibited"/>
<attribute name="opaque" type="bpws:tBoolean"
use="prohibited"/>
<attribute name="endpointReference" type="bpws:tRoles"
use="prohibited"/>
</restriction>
</complexContent>
</complexType>
</element>
<complexType name="tWait">
<complexContent>
<extension base="bpws:tActivity">
<attribute name="for" type="bpws:tDuration-expr"/>
<attribute name="until" type="bpws:tDeadline-expr"/>
</extension>
</complexContent>
</complexType>
<complexType name="tThrow">
<complexContent>
<extension base="bpws:tActivity">
<attribute name="faultName" type="QName" use="required"/>
<attribute name="faultVariable" type="NCName"/>
</extension>
</complexContent>
</complexType>
<complexType name="tCompensate">
<complexContent>
<extension base="bpws:tActivity">
<attribute name="scope" type="NCName"/>
</extension>
</complexContent>
</complexType>
<complexType name="tTerminate">
<complexContent>
<extension base="bpws:tActivity"/>
</complexContent>
</complexType>
<complexType name="tFlow">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="links" type="bpws:tLinks" minOccurs="0"/>
<group ref="bpws:activity" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tLinks">
<complexContent>
<extension base="bpws:tExtensibleElements">
<sequence>
<element name="link"
type="bpws:tLink"
maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tLink">
<complexContent>
<extension base="bpws:tExtensibleElements">
<attribute name="name" type="NCName" use="required"/>
</extension>
</complexContent>
</complexType>
<complexType name="tSwitch">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="case" maxOccurs="unbounded">
<complexType>
<complexContent>
<extension base="bpws:tActivityContainer">
<attribute name="condition"
type="bpws:tBoolean-expr"
use="required"/>
</extension>
</complexContent>
</complexType>
</element>
<element name="otherwise"
type="bpws:tActivityContainer"
minOccurs="0"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tWhile">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<group ref="bpws:activity"/>
</sequence>
<attribute name="condition"
type="bpws:tBoolean-expr"
use="required"/>
</extension>
</complexContent>
</complexType>
<complexType name="tSequence">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<group ref="bpws:activity" maxOccurs="unbounded"/>
</sequence>
</extension>
</complexContent>
</complexType>
<complexType name="tPick">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="onMessage"
type="bpws:tOnMessage"
maxOccurs="unbounded"/>
<element name="onAlarm"
type="bpws:tOnAlarm" minOccurs="0"
maxOccurs="unbounded"/>
</sequence>
<attribute name="createInstance"
type="bpws:tBoolean" default="no"/>
</extension>
</complexContent>
</complexType>
<complexType name="tScope">
<complexContent>
<extension base="bpws:tActivity">
<sequence>
<element name="variables"
type="bpws:tVariables"
minOccurs="0"/>
<element name="correlationSets"
type="bpws:tCorrelationSets"
minOccurs="0"/>
<element name="faultHandlers"
type="bpws:tFaultHandlers"
minOccurs="0"/>
<element name="compensationHandler"
type="bpws:tCompensationHandler"
minOccurs="0"/>
<element name="eventHandlers"
type="bpws:tEventHandlers"
minOccurs="0"/>
<group ref="bpws:activity"/>
</sequence>
<attribute name="variableAccessSerializable"
type="bpws:tBoolean"
default="no"/>
</extension>
</complexContent>
</complexType>
<simpleType name="tBoolean-expr">
<restriction base="string"/>
</simpleType>
<simpleType name="tDuration-expr">
<restriction base="string"/>
</simpleType>
<simpleType name="tDeadline-expr">
<restriction base="string"/>
</simpleType>
<simpleType name="tBoolean">
<restriction base="string">
<enumeration value="yes"/>
<enumeration value="no"/>
</restriction>
</simpleType>
<simpleType name="tRoles">
<restriction base="string">
<enumeration value="myRole"/>
<enumeration value="partnerRole"/>
</restriction>
</simpleType>
</schema>
Partner Link
Type Schema
<?xml version='1.0' encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
xmlns:plnk="http://schemas.xmlsoap.org/ws/2003/05/partner-link/"
targetNamespace="http://schemas.xmlsoap.org/ws/2003/05/partner-link/"
elementFormDefault="qualified">
<element name="partnerLinkType" type="plnk:tPartnerLinkType"/>
<complexType name="tPartnerLinkType">
<sequence>
<element name="role" type="plnk:tRole" minOccurs="1" maxOccurs="2"/>
</sequence>
<attribute name="name" type="NCName" use="required"/>
</complexType>
<complexType name="tRole">
<sequence>
<element name="portType" minOccurs="1" maxOccurs="1">
<complexType>
<attribute name="name" type="QName" use="required"/>
</complexType>
</element>
</sequence>
<attribute name="name" type="NCName" use="required"/>
</complexType>
</schema>
Message
Properties Schema
<?xml version='1.0' encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
xmlns:wsbp="http://schemas.xmlsoap.org/ws/2003/03/business-process/"
elementFormDefault="qualified">
<element name="property">
<complexType>
<attribute name="name" type="NCName" use="required"/>
<attribute name="type" type="QName" use="required"/>
</complexType>
</element>
<element name="propertyAlias">
<complexType>
<attribute name="propertyName" type="QName" use="required"/>
<attribute name="messageType" type="QName" use="required"/>
<attribute name="part" type="NCName"/>
<attribute name="query" type="string"/>
</complexType>
</element>
</schema>E. Notices
Copyright © The Organization for
the Advancement of Structured Information Standards [OASIS] 2001, 2002, 2003.
All Rights Reserved.
OASIS takes no position regarding
the validity or scope of any intellectual property or other rights that might
be claimed to pertain to the implementation or use of the technology described
in this document or the extent to which any license under such rights might or
might not be available; neither does it represent that it has made any effort
to identify any such rights. Information on OASIS's procedures with respect to
rights in OASIS specifications can be found at the OASIS website. Copies of
claims of rights made available for publication and any assurances of licenses
to be made available, or the result of an attempt made to obtain a general
license or permission for the use of such proprietary rights by implementors or
users of this specification, can be obtained from the OASIS Executive Director.
OASIS invites any interested
party to bring to its attention any copyrights, patents or patent applications,
or other proprietary rights which may cover technology that may be required to
implement this specification. Please address the information to the OASIS
Executive Director.
This document and translations of
it may be copied and furnished to others, and derivative works that comment on
or otherwise explain it or assist in its implementation may be prepared,
copied, published and distributed, in whole or in part, without restriction of
any kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this document itself
may not be modified in any way, such as by removing the copyright notice or
references to OASIS, except as needed for the purpose of developing OASIS
specifications, in which case the procedures for copyrights defined in the
OASIS Intellectual Property Rights document must be followed, or as required to
translate it into languages other than English.
The limited permissions granted
above are perpetual and will not be revoked by OASIS or its successors or
assigns.
This and the information
contained and the information is provided on an "AS IS"
basis and DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO WARRANTY THAT THE USE OF THE INFORMATION HEREIN NOT INFRINGE ANY
RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE.
OASIS has been notified of
intellectual property rights claimed in regard to some or all of the contents
of this specification. For more information consult the online list of claimed
rights.
F. Intellectual
Property Rights
For information on wether any
patents have been disclosed that may be essential to implementing this
specification, and any offers of patent licensing terms, please refer to the
Intellectual Property Rights section of the WS-BPEL Technical Committee web
page (http://www.oasis-open.org/committees/wsbpel)
G. Revision
History
|
Revision 01 |
xx June 2003 |
TBS |
|
TBS |
||
|
Revision 00 |
10 June 2003 |
PY |
|
First Draft.
Produced from |
||
Normative
[XMLSpec] XML Specification,
W3C Recommendation.
[SOAP 1.1] Simple Object Access Protocol
(SOAP) 1.1, W3C Note
[WSDL 1.1] Web Services Definition
Language (WSDL) 1.1, W3C Note
[UDDI] Universal Description, Discovery and Integration,
Industry Initiative
[XML Schema Part 1] XML Schema Part 1:
Structures, W3C Recommendation
[XML Schema Part 2] XML Schema Part 2:
Datatypes, W3C Recommendation
[XPATH 1.0] XML Path Language (XPath)
Version 1.0, W3C Recommendation
[Trends] Trends in
systems aspects of database management," I.L. Traiger, Proc. 2nd Intl. ,
Conf. on Databases (ICOD-2), Wiley and Sons 1983.
[RFC 2119] RFC 2119: Key words
for use in RFCs to Indicate Requirement Levels, S. Bradner. IETF
(Internet Engineering Task Force), 1997.
[RFC 2396] RFC 2396: Uniform
Resource Identifiers (URI): Generic Syntax, T. Berners-Lee, R.
Fielding, L. Masinter, MIT/LCS, U.C. Irvine, Xerox Corporation, August 1998.
[BPEL4WS 1.0] Business
Process Execution Language for Web Services Version 1.0, BEA,
[WS-Addressing] Web
Services Addressing (WS-Addressing), BEA,
H. Committee
Members (Non-Normative)
The following individuals were
members of the committee during the formulation of this document:
·
Lars Abrell
·
Ravi
Akireddy
·
Hedy
Alban
·
Randall
Anderson, Macgregor
·
·
Assaf
Arkin,Intalio
·
Sid
Askary
·
Kent
Below,
·
Terry
Bjornsen, Booz Allen Hamilton
·
Mike
Blevins, BEA
·
·
Alex
Boisvert, Intalio, Inc.
·
Subhra
Bose, Reuters America
·
George
Brown,
·
Steve
Brown, Metastorm
·
Justin
Brunt, WfMC
·
Navin
Budhiraja, Vitria
·
David
Burdett, CommerceOne
·
Laurence
Cable
·
Ryan
Cairnsi, OpenStorm Software
·
Arun
Candadai
·
fred
carter, AmberPoint
·
Andy
Chan, FileNet
·
Sarat
Chand,
·
Chia
Chao, IONA
·
Martin
Chapman,
·
Dave
Chappell, Sonic Software
·
Jamie
Clark, OASIS
·
Doron
Cohen, BMC Software
·
Ugo
Corda, SeeBeyond
·
Robin
Cover, OASIS
·
Fred
Cummins,
·
Francisco
Curbera,
·
Sanjay
Dalal, BEA
·
Khoi
Dang, FileNet
·
Michael
DeBellis, Fujitsu
·
Linda
DeMichiel,
·
Jens
Doerpmund, Hewlett-Packard
·
Bernd
Eckenfels, Seeburger, AG
·
Rami
Elron, BMC Software
·
·
B.J.
Fesq
·
Rabih
Filfili, Microsoft
·
Layna
Fischer, BPMI.org
·
Layna
Fischer, WfMC
·
Tony
Fletcher, Choreology
·
Bill
Flood, Sybase
·
Daniel
Foody, Actional
·
Steven
Forgey, SeeBeyond
·
Franz
Fritz,
·
Yuzo
Fujishima,
·
Shoichi
Fukuda, Fujitsu
·
Peter
Furniss, Choreology
·
Jean-Luc
Giraud, Axway software
·
Yaron
Goland, BEA
·
Alastair
Green, Choreology
·
Ajay Gummadi
·
Michael
Hafner,
·
Tommy
Hansen, FileNet
·
Kevin
Hein, Teamplate
·
Scott
Hinkelman,
·
Chunbo
Huang, BEA
·
Yin-Leng
Husband, Hewlett-Packard
·
David
Ingham, Arjuna Technologies
·
Ram
Jeyaraman,
·
Diane
Jordan,
·
Bala
Kamallakharan, Cap Gemini Ernst and Young
·
Neelakantan
Kartha, Sterling Commerce
·
Nicholas
Kassem,
·
Nickolas
Kavantzas,
·
Michael
Keay
·
Debra
Kellington, Convergys
·
Edwin
Khodabakchian, Collaxa
·
·
Yoav
Kirsch, Business Layers
·
Melanie
Kudela, Uniform Code Council
·
Pradeep
Kumar, MRO Software
·
Sanjeev
Kumar
·
·
Kelvin
Lawrence,
·
Philip
Lee, BPMI.org
·
Frank
Leymann,
·
Yanming
Li, France Telecom
·
Paul
Lipton, Computer Associates
·
Mark
Little, Arjuna Technologies
·
Melton
Littlepage, Booz Allen Hamilton
·
Kevin
Liu,
·
Brian
Lorenz, Sybase
·
Hop
Luu, FileNet
·
Art
Machado,
·
Balinder
Malhi, Microsoft
·
Sumeet
Malhotra, Unisys
·
Rajesh
Manglani, Uniform Code Council
·
Bernard
Manouvrier, Axway software
·
Mike
Marin, FileNet
·
Monica
Martin,
·
Tod
Matola, Sterling Commerce
·
carol
mcdonald,
·
·
Vinkesh
Mehta, CommerceOne
·
Glenn
Mi, Collaxa
·
Jeff
Mischkinsky,
·
JP
Morgenthal, Software AG
·
Tim
Moses, Entrust
·
Kenji
Nagahashi, Fujitsu
·
Trevor
Naidoo, IDS Scheer
·
Goran
Olsson,
·
Srinivas
Padmanabhuni, Infosys
·
John
Parkinson, Cap Gemini Ernst and Young
·
Sanjay
Patil, IONA
·
Mark
Potts, Talking Blocks
·
Rajesh
Pradhan, Iopsis Software
·
Matthew
Pryor, BPMI.org
·
Ken
Pugsley,
·
Andrew
Pugsley, Hewlett-Packard
·
Jon
Pyke, WfMC
·
Harvey
Reed, Sonic Software
·
Sundari
Revanur, IONA
·
Greg
Ritzinger,
·
Anthony
Roby,
·
Jorge
Rodriguez,
·
Dieter
Roller,
·
Darran
Rolls, Waveset Technologies
·
Phil
Rossomando, Unisys
·
Steve
Ross-Talbot, Enigmatec
·
Michael
Rowley, BEA
·
Waqar
Sadiq,
·
Yuji
Sakata
·
Krishna
Sankar,
·
Bob
Schmidt, Microsoft
·
Marc-Thomas
Schmidt,
·
Yoko
Seki, Hitachi
·
Pinaki
Shah, E2Open
·
Vishwanath
Shenoy, Infosys
·
Frank
Siebenlist, Argonne National Laboratory
·
Parijat
Sinha, Convergys
·
Dale
Skeen, Vitria
·
Howard
Smith, BPMI.org
·
Gavenraj
Sodhi, Business Layers
·
Vinay
Srinivasaiah, SeeBeyond
·
Venkat
Srinivasan, SeeBeyond
·
Nallan
Sriraman, Reuters America
·
Sally
St. Amand
·
Donald
Steiner, WebV2
·
Karl-Heinz
Sternemann, BizTalk Competence Center
·
Nikola
Stojanovic
·
Keith
Swenson, Fujitsu
·
Maciej
Szefler, FiveSight Technologies
·
Pal
Takacsi-Nagy, BEA
·
Ran
Tamir, BMC Software
·
Bob
Taylor, Hewlett-Packard
·
Sazi
Temel, BEA
·
Ron
Ten-Hove,
·
Aniruddha
Thakur,
·
·
Steve
Towers, BPM Group
·
Derick
Townsend, OpenStorm Software
·
Ivana
Trickovic,
·
Kenwood
Tsai, Documentum
·
William
Vambenepe, Hewlett-Packard
·
Danny
van der Rijn, Tibco
·
Gloria
Vargas, Reuters America
·
Ganesh
Vednere, Cap Gemini Ernst and Young
·
Claus
von Riegen,
·
Jim
Webber, Arjuna Technologies
·
David
Webber
·
Michael
Weiner,
·
Pete
Wenzel, SeeBeyond
·
Stuart
Wheater,Arjuna Technologies
·
Stephen
White
·
·
Prasad
Yendluri, webMethods
·
Eric Yuan,
Booz Allen Hamilton
·
Sinisa
Zimek,
·
Michael
zur Muehlen, WfMC