Re: [wsbpel] Issue 82 - Adding requesting clarifications (with changelog)

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

Hi everyone,

Monica, Ron, Peter, and I took a stab at incorporating Monica and Ron's requested clarifications with my response and Peter's text on 82. We tried very hard to ensure that changes  clarify/make consistent the text below *without changing the content and  intent*.

This text is provided  for consideration,  as input towards addressing the TC's request that requested clarifications be handled before 82 can be closed.

I will also send a version without the change log that should be easier to read from start to finish.

Best Regards,
Rania (w/ Monica, Ron, and Peter).

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key:
 red = changes. (Additions, unless otherwise specified.)
**addressing (x)** precedes each, where (x) is the item number from Monica and Ron's email of concerns.
---------------------------------------------

**addressing (4)**
IMPORTANT NOTE ON 82:
--------------------------------
Ambiguities should be limited/focus on non-substantive changes to  the accepted concept,  i.e. editorial comment, further clarification that do not change the substance of the accepted proposal from Peter dated 12/15/2004.

Proposal for Issue 82:  

Abstract BPEL definition:

A BPEL abstract process is a partially specified process that is not intended to be executed. Executable and abstract BPEL processes share the same expressive power, while the latter allows process definitions that are capable of abstracting away operational details _ either through omission or explicit opacity.  Whereas executable processes are fully concretized and thus can be executed, an abstract process

              may

 lack some of the required concrete operational details expressed by

**addressing (a)**
deleted: "or when mapping it to "

a fully executable artifact. An abstract BPEL process must be explicitly declared as 'abstract'.

Abstract processes serve a descriptive role, with more than one possible purpose. 

**addressing (b,c)**
Replace: A BPEL abstract process can
Wiith:     One such purpose for an abstract process could be

to define the publicly visible behavior of some or all of the services it offers ("myRole" in its partnerLinks), which may include its interactions along its partnerLinks with other services.

**addressing (b,c)**
Replace: Alternatively, a BPEL abstract process

With:      Another purpose could be to

define a process "template" embodying domain-specific best practices, encoded in a platform-neutral and portable way by both enterprises and vertical standards organizations.

**addressing (b,c)**
Replace: The process "template" captures some essential process logic while leaving out operational details that will be concretized by the enterprises and vertical standards organizations when mapping the partial process specification to a fully executable artifact.

With:      For example, a  process "template" could capture some essential process logic while leaving out operational details that will be concretized when mapping the partial process specification to a fully executable artifact.

The different uses of abstract BPEL require different levels of opacity and restrictions or relaxations on which elements of a corresponding executable artifact are omitted or hidden.  To cleanly enable different usages of abstract processes, an extensible approach is taken using a set of basic, minimal requirements (base) for all abstract processes.

**addressing (d)**
Replace:  From this base, "usage profiles" can be defined. On its own, the base lacks well-defined semantics - the only constructs that have defined meaning are the constructs of executable processes, and that meaning is defined by prescribed behaviour of the executable process as a whole, and is thus not directly available outside an executable process.

With:      The abstract process base definition lacks well-defined semantics. Conversely, executable processes have well-defined semantics and prescribed behavior. From the abstract process base definition, "usage profiles" can be defined.

 The semantics of an abstract process are therefore derived from those of the executable

**addressing (e)**
Replace: process it could be mapped to.
With: processes to which it would be mapped.

To define these semantics, the range of corresponding executable processes can be constrained by a usage profile, placing constraints on what is opaque or omitted.  An abstract process  MUST identify the usage profile  that defines its meaning.

**clarification**
Replace:   with a URI.
With:       The profile is identified using a URI.

**addressing (e)**
Replace:  Profiles may be defined by anyone - in separate standardization efforts, internally in organizations or for proprietary usage, etc. 
With: Where profiles are defined is left unspecified.

 

**addressing (1,2)**
The base is simply a set of minimum requirements for all abstract processes. Profiles are created from the base. One or two profile(s) will be given in the specification. They/it will show how one can create a profile by building on the base. 

[The TC will rework the 1.1 AP definition into a profile with a defined URI. 

**addressing: (1,2,3,f) **
REPLACE: [It is left open, at the moment, whether the base definition itself is to be considered as a profile. If it is, it will be assigned a URI to identify it] )
WITH:
It is left open whether another profile will be defined in the specification that is identical to the base. If so, it will be given a URI to identify it and added. It is suggested that a separate, new issue XX be opened for this. The dependency (by allowed closing order) of these three issues is: 82, XX, 158. 

The placement of these profiles and other questions concerning the structure of the ultimate specification and how many documents there will be will be left open and dealt with as part of 158]

**addressing (e, 3)**
Issue 158 cannot be closed until 82 is closed.

 Semantics of Abstract Processes:

[1] Although it might contain complete information that would render it executable as specified for executable BPEL, its abstract status states that any concrete realizations of it may perform additional processing steps that are not relevant to the audience to which it has been given. The minimum criteria for an abstract process is defined in this specification while completeness is left to the usage profile a particular abstract process definition belongs to.

[2] Abstract processes permit the use of all of the constructs of executable processes. Thus there is no fundamental expressive power distinction between abstract and executable processes.

[3] An abstract process may omit operational details that are mandatory for BPEL executable processes through the use of "opaque" entities of various types (i.e. elements, attributes, etc.) or through the omission of specific BPEL elements or attributes that are allowed to be implicitly opaque. This omission is treated as a syntactic shortcut equivalent to the attribute or expression being in the omitted location with an opaque value.

The semantics and consistency constraints of executable BPEL are clearly defined. The semantics of each

**addressing (g) **
language

construct in an abstract process

**addressing (g) **
are always

 derived from that of the same construct in executable BPEL.

**addressing (g) **
(i.e. an invoke is always an invoke).

The difference is strictly a consequence of the opacity used in that construct (missing information) and other parts of the process affected by it ( For example, opacity in a link source element may affect the link target element).

**addressing (h)**
Replace: Addionally, an abstract process is required to be syntactically valid using the executable schema extended with the opaque entities.
With:      Additionally, an abstract process is required to be syntactically valid using the BPEL schema, that accommodates extension with opacity and omissions as detailed in bullet 3 above. One schema exists for abstract and executable BPEL. (Check that this is consistent with resolution of 24).

[4] In this base definition, to avoid absurd constructs and to clarify opacity, the minimial requirement is that for any abstract process, there exists at least one syntactic completion that yields a *valid executable process* by

    a) replacing each opaque token by a concrete entity or removing the opaque token completely, and

    b) adding new BPEL XML elements anywhere in the process.

**addressing (j)**
This is used for checking the syntactic validity of an abstract process not for process semantics.

[5] For this base definition, there are no requirements on how concretized, executable realizations of abstract process should be implemented (ie: language, platform, etc) (c.f. analogy to WSDL); nor are specific relationships with such realizations specified.

[6] Abstract processes are *incomplete* and non-executable by definition, whether or not they contain opaque entities. Therefore the semantics of the non-opaque constructs they contain cannot be understood in isolation from the relationship of the abstract process with the executable *completions*

**addressing (k)**
Replace: it permits
With:      that are permitted by the profile the abstract process references.

The reason being that the semantics of those constructs actually exists only in the possible executable completions. As an edge case, a permitted completion may sometimes be identical to the abstract process syntactically, but this is the exception rather than the rule.

__

 

Peter

 

------------------------------------------
Peter Furniss
Chief Scientist, Choreology Ltd
web: http://www.choreology.com
email: peter.furniss@choreology.com
phone: +44 870 739 0066
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