Re: [wsbpel] 82.3 updated to reflect amendments (w minor clarification)

[Rania Khalaf <rkhalaf@watson.ibm.com>]

Hi guys,

here is the updated version. Alex, I fiddled a bit more with the text on 
assign and endpoint references to make it clearer because 'an assign 
activity or otherwise MUST NOT' puts the focus on 'otherwise' and 
'assign' so I think the new text is clearer yet still uses MUST NOT as 
you suggested.


the text there now reads:

•	The endpoint reference of any partnerLink defined in the abstract 
process MUST NOT be modified (whether using an <assign> activity or 
otherwise). Additionally, an endpoint reference of any partnerLink 
defined in the abstract process MUST NOT be copied into the reference of 
a newly created partnerLink.  The reason is that the former would 
effectively prevent subsequent interactions with that partner and the 
latter would add new ones.  Remember that 'opaque token replacement'
also replaces opaque tokens omitted through the omission-shortcut.

This and the rest of the changes are in the attached document.


Diane Jordan wrote:
>  
> 
> Change busines sprotocol to behavior contracts
> 
> Change must not back to caps
> This section clarifies the meaning of using opacity of variables in 
> interaction activities. If _a _no variable_ reference_ is _opaque 
> _specified i_i_n a_n_n _inbound _interaction _message _activity which 
> receives an incoming message, then the abstract process _must not – and 
> has no way to - _MUST NOT subsequently_subsequently_ refer to the 
> received message or its properties, if any. If _a_the variable reference 
> is omitted _opaque _for an _outbound message _activity that sends an 
> outgoing message, then_ each executable completion must have already 
> initialized the _ any properties of the message_ that gets used by that 
> activity._ are considered to have been initialized through opaque 
> assignment,
> 
> Delete these paragraphs:  
> 
> When variable references are _opaque_omitted in interaction _message 
> _activities, correlation set references may be interpreted as follows: 
> _[ryk1]_ 
> <http://www.oasis-open.org/apps/org/workgroup/wsbpel/email/archives/200510/msg00102.html#_msocom_1>  
> 
> 
>  
> 
> 1.      When an incoming message initializes a correlation set 
> (initiator case), the correlation set is considered to be initialized.
> 
> 2.      When an outgoing message initializes a correlation set 
> (initiator case), the correlation tokens (message _(_properties) _must 
> be_are initialized _in any executable completion. _through an implicit 
> opaque assignment.
> 
> 3.      For an outgoing message which references but does not initialize 
> a correlation set (follower case), the proper initialization of the_ 
> _ message properties _ must be done in the executable completions. _is 
> implicit. In this case, the already initialized correlation set itself 
> provides the token values for the outgoing message.
> 
> It is not possible to arbitrarily mix interaction _message _activities 
> that use variable references with those that don’t. If a correlation set 
> is initialized by rules 1 or 2 above, then outgoing messages using the 
> same correlation set 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.
> 
> o Change from: "It is not allowed to modify (in an
>                 <assign> activity or otherwise) the endpoint reference
>                 of a partnerLinks..."
>               o Change to: "An <assign> activity or otherwise MUST NOT
>                 modify the endpoint reference of a partnerLinks..."
> 
> 
> 
> Regards, Diane
> IBM  Emerging Internet Software Standards
> drj@us.ibm.com
> (919)254-7221 or 8-444-7221, Mobile: 919-624-5123, Fax 845-491-5709
>

Title: Web Services Business Process Execution Language

15. WS-BPEL Abstract Processes  

 <insert 82 base text >

…

15.3 Abstract Process Profile for Observable Behavior

Motivation

The objective of the Abstract Process Profile for Observable Behavior is to provide precise and predictable descriptions of observable service behavior. The main application of this profile is the definition of business process protocolscontracts, that is, the protocol behavior followed by one business partner in the context of a Web services exchange. Business process protocols contracts are particularly relevant in automated cross-enterprise interactions, including business-the area e-commerce, but have general applicability in the extension of service contracts with precise, machine processable behavioral descriptions.

There several a key differences between processes intended to represent business process protocolcontracts and fully executable processes. Foremost among them is the different way in which data are handled in each case; the rich data manipulation that occurs in executable processes need not be described in public process protocolscontracts. Instead, public process protocols contracts use non-deterministic data values to hide the private aspects of executable behavior. For example, using opaque assignment supports modeling the non-deterministic effects that private computation has on external behavior.

In this profile, the use of opacity is consequently concentrated in those features associated with data handling. Non-deterministic data values are not allowed in executable processes;  abstract processes, on the other hand, use non-deterministic values to reflect the consequences of actual behavior while maintaining the details of that behavior private.

Profile URI

The URI identifying this abstract process profile is:

 

urn:oasis:names:tc:wsbpel:2.0:abstract:ap11<year><month>

 

Subset of the Processes Allowed in the Base

This profile is concerned mainly with hiding internal processing of a business partner while capturing all the information required to describe how the process interacts with its partners. The set of usage restrictions associated with the use of abstract processes in general was in fact derived from this original requirement, which was captured by the Abstract Process definition incorporated in the previous version of this specification (BPEL4WS V1.1, May 2003).

 

It has been mentioned already that this profile applies opacity in BPEL constructs that handle data. In addition, the omission-shortcut described in section 15 can be used as an alternative to explicitly specifying opaque tokens.  opaque tokens are allowed to be omitted using the omission-shortcut described in section 15. 

 

 

The profile described here allows the use of opaque activities for supporting the specific case where an activity is syntactically required.The profile described here allows the use of opaque activities The first is for supporting two specific tasks. First is the  hiding of a non-opaque activity that is the source or target of one or more links in an executable process from which a business process contractprotocol is defined, while maintaining the same flow of control in the abstract representation. .The secondSecond, is the use of the omission shortcut in places where an activity is required by the BPEL semantics and schema (e.g., activity in a fault handler; this usage obviates the way instead of requiring one to add an <empty> just to satisfy the schema). The use of opaque activities where an activity is not syntactically required elsewhere iis superfluous, because this profile’s completion rules are flexible about where one can add an activity in an executable completion. The full completion rules are presented in the next section.

 

This profile restricts the use of the Abstract Process Base in the following manner:

 

·        Expressions: joinCondition is not allowed to be opaque. The joinCondition is based on the transition conditions of the incoming links, with a default value being the disjunction of the status of those links, and not on data handled by the process.  Therefore, it is not appropriate to hide it. Other expressions may be opaque, as defined in section 15.

·        Activities: The use of <exit > is not allowed.

·        Attributes:  Only the attributes used for identification of data containers of activities  representing partner interactions are allowed to be opaque. Note that assigning to opaque containers is already available using the opaque assignment capability discussed in section 15, where one assigns from an opaque expression. The full list of the attributes allowed to be opaque is shown below. The following is the complete list of attributes, belonging to the receive, invoke, reply, onMessage, or onEvent constructs, that are allowed to be opaque in this profile:

o       "variable", "inputVariable", "outputVariable",

o       "part" and "toVariable" attributes of  the "fromPart" element,

o       "part" and "fromVariable" attribute of "toPart"

 

The level of abstraction appropriate in the description of business process contractprotocols makes it often unnecessary to use message variables in Web service interaction message activities, particularly when the intent is to simply constrain the sequencing of such activities and the actual message data is not relevant.

 

 

Subset of the Executable Completions Allowed in the Base

With respect to executable BPEL completions of an abstract process that uses this profile, the intent of the profile requires a valid completion to follow the same interactions as the abstract process, with the partners that are specified by the abstract process. The executable process may, however, perform additional interaction steps relating to other partners.

 

Therefore: a completion MUST NOT change the presence or order of interactions already in the abstract process, and it MUST NOT perform additional interactions with the partner links defined in the abstract process. It is important to observe that one way in which the order of interactions can be modified is by changing the value of a variable used in a condition that affects branching in such a way that the new effective branching behavior is in direct conflict with what is specified by the abstract process. Conditions that affect the flow of control such as transition conditions, “if-then” or “while” expressions, among others, can have such an effect on the order of interactions. For example, adding a new <while> loop with a “true” condition as a child of an existing <sequence> would hang the process.  In this profile, we will not restrict writing to variables in a strict manner, but provide this note as an advisory restriction.

 

The possible locations of new activities are not explicitly defined in this profile. Activities may be added anywhere where completions to the base are allowed, as long as the restrictions enumerated below are followed. In this profile, the valid executable completions of an abstract process are obtained through both 'opaque token replacement' and 'addition of BPEL constructs', with the following restrictions:

 

·        New activities (including those created to replace opaque activities) MUST NOT interact with partnerLinks already defined in the abstract process. This rule does not affect adding interactions with new partnerLinks present in the executable completion but not in the abstract process.

 

·        The endpoint reference of any partnerLink defined in the abstract process MUST NOT be modified It is not allowed to modi(whether using an <assign> activity or otherwise). Additionally, fy (in an <assign> activity or otherwise) the endpoint reference of partnerLinks defined in the abstract process,an endpoint reference of any partnerLink defined in the abstract process MUST NOT be copied into the reference of a newly created partnerLink.  because t The reason is that the formerat would effectively prevent subsequent interactions with that partner and the latter would add new ones.  Remember that 'opaque token replacement' also replaces opaque tokens omitted through the omission-shortcut.

 

·        The lexical parent an existing BPEL construct (including activities in particular) present in the abstract process MUST NOT be changed in a valid executable completion. Hence, the nesting structure of composite activities around any activity in an abstract process MUST remain unchanged in any legal completion. Some examples to illustrate this restriction are provided below. The word ‘existing’ is used in the examples to refer to constructs defined in the abstract process from which the executable completions are being created:

o       Examples of legal additions:

§         Adding a variable or a partner link to an existing scope S, even though that scope is the parent of existing activity A.

§         Adding a new link def to an existing flow.

o       Examples of illegal additions:

§         Adding a <while> activity around the existing activity A whose parent is another existing activity B.

§         Adding a new scope around an existing variable definition whose parent is an existing scope S.

 

·        A valid executable completion MUST NOT add:

o       New branches to an existing “if-then-else” activity, unless it has no “else” branch, and the new branch is added after all existing branches.

o       New branches to an existing pick activity.

o       New fault, compensation, or termination handlers to an existing scope. However, they may be added at the process level.

o       <exit> activities.

 

·        Activities that throw non-standard faults MAY be added only if the exception will not be propagated outside of the highest newly added ancestor of the fault-throwing activity.  For example, consider adding an activity A as a child of an existing sequence S.  Then, one may only add a <throw> within A if the fault it throws does not reach the scope of the existing sequence S. In other words, the fault must be caught and fully handled by A or its descendants, and not be re-thrown by them.

 

Observe that executable completions MUST NOT add new links targeting an activity that exists in the abstract process. Adding such a new link would have the effect of changing the corresponding join condition, which is in violation of the completion rules of the base (since it modifies a non-opaque existing value). This restriction does not affect the addition of links to new activities that are not replacing opaque activities.

 

Clarification on tThe Uuse of Opaque Variable References

Unlike executable processes, variables in abstract processes defined using this profile do not need to be fully initialized before being used since additional computation may be implicitly assumed. However, since message properties are meant to represent "transparent" or , or protocolprocess contract relevant, data, all message properties in a message MUST be initialized in an executable completion before the message can be used.

In particular, all properties in a message need to be initialized before a variable containing the message is used as the inputVariable in a Web service invocation.

 

This section clarifies the meaning of using opacity of variables in interaction activities. If a no variable reference is opaque specified iin ann inbound interaction message activity which receives an incoming message, then the abstract process MUST NOT – and has no way to - MUST NOT subsequentlysubsequently refer to the received message or its properties, if any. If athe variable reference is omitted opaque for an outbound message activity that sends an outgoing message, then each executable completion must have already initialized the  any properties of the message that gets used by that activity. are considered to have been initialized through opaque assignment,

 

When variable references are omitted in interaction activities, correlation set references may be interpreted as follows: [ryk1] 

 

1.When an incoming message initializes a correlation set (initiator case), the correlation set is considered to be initialized.

2.0.When an outgoing message initializes a correlation set (initiator case), the correlation tokens (message properties) are initialized through an implicit opaque assignment.

3.0.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.

 

It is not possible to arbitrarily mix interaction activities that use variable references with those that don’t. If a correlation set is initialized by rules 1 or 2 above, then outgoing messages using the same correlation set 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.

16. Examples

16.1. Shipping Service: Abstract Process, Observable Behavior Profile

This example presents the use of a WS-BPEL 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 shipments where the items are shipped piecemeal until all of the order is accounted for.

16.1.1. Service Description

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">

        <plnk:role name="shippingService" 

                   portType ="shippingServicePT"/>

        <plnk:role name="shippingServiceCustomer">

                   portType ="shippingServiceCustomerPT"/>

</plnk:partnerLinkType>

The corresponding message and portType definitions are as follows:

<wsdl:definitions

        targetNameSpace="http://ship.org/wsdl/shipping"

        xmlns:ship= ...> 

        <! -- import ship schema -- >

        <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>

16.1.2. Message Properties

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:ship = “http://example.com/ship.xsd”>

<!-- types used in abstract processes are required to be finite domains.

      The itemCountType is restricted by range -->

        <wsdl:types>

             <xsd:schema targetNamespace=“http://example.com/ship.xsd”>

               <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

           </query>

        </bpws:propertyAlias>  

        <bpws:propertyAlias propertyName="tns:shipOrderID"

              messageType="sns:shippingNoticeMsg"

              part="shipNotice">

           <query>

           ShipNoticeHeader/shipOrderID

           </query>

        </bpws:propertyAlias>          

        <bpws:propertyAlias propertyName="tns:shipComplete"

              messageType="sns:shippingRequestMsg"

              part="shipOrder">

          <query>

          ShipOrderRequestHeader/shipComplete

          </query>

        </bpws:propertyAlias>  

        <bpws:propertyAlias propertyName="tns:itemsTotal"

              messageType="sns:shippingRequestMsg"

              part="shipOrder">

           <query>

           ShipOrderRequestHeader/itemsTotal

           </query>

        </bpws:propertyAlias>  

        <bpws:propertyAlias propertyName="tns:itemsCount"

              messageType="sns:shippingNoticeMsg"

              part="shipNotice">

           <query>

           ShipNoticeHeader/itemsCount

           </query>

        </bpws:propertyAlias>

</wsdl:definitions>

16.1.3. Process

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

if

        condition shipComplete

             send shipNotice

        else

             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/2004/03/business-process/"

        xmlns:sns="http://ship.org/wsdl/shipping"

        xmlns:props="http://example.com/shipProps/"        abstractProcessProfile="urn:oasis:names:tc:wsbpel:2.0:abstract:ap11<year><month>

">

<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>

    <if>

      <condition>

      bpws:getVariableProperty('shipRequest','props:shipComplete')

      </condition>

        <then>

          <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>

        </then>

        <else>

           <sequence>

               <assign>

                  <copy>

                       <from>0</from>

                       <to>$itemsShipped</to>

                 </copy>

               </assign>

               <while>

                  <condition> 

                  $itemsShipped <

        bpws:getVariableProperty('shipRequest','props:itemsTotal')

                  </condition>

                  <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>

                               $itemsShipped

                               +

                               bpws:getVariableProperty('shipNotice',

                               'props:itemsCount')

                               </from>

                               <to>$itemsShipped</to>

                          </copy>

                       </assign>

                  </sequence>

                 </while>

             </sequence>

          </else>

        </if>

</sequence>

</process>

---

 [ryk1]A variable, property, or correlation set used in the AP is considered to have been already initialized.