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Subject: [NEW ISSUE] BPEL Process: References with Multiplicity 0..1 - how are theysupposed to work?

Raiser:                Mike Edwards



Multi-valued references (ie 0..n and 1..n) are discussed in the specification at some length, particularly in section
3.2.  Unfortunately, the case of 0..1 references is mentioned only in passing, although it has some significant

matters that need discussion and clarification.

Section 2.1.1 makes it clear that 0..1 multiplicity references do exist for BPEL processes.

Basically, it states that where a partnerLink is determined to be a reference, it will be 0..1 if @initializePartnerRole="no"

OR @initializePartnerRole is omitted.  It must also be the case that the partnerLink must not have its "first use" as the

target of an <assign/> operation.

Now, reading the BPEL 2.0 specification:

   @initializePartnerRole="no" means that the BPEL Processor MUST NOT initialize the partnerLink variable.

   @initializePartnerRole omitted means that the BPEL Processor MAY initialize the partnerLink variable.

Now, the problems are these:

A)  If the partnerLink is NOT initialized, then it is essential that it is initialized by the BPEL process itself, since any

attempt to use that partnerLink variable will otherwise result in a fault.

So, if the partnerLink is marked @initializePartnerRole="no", the partnerLink must be supplied with a value - but

how is such a value supplied to the BPEL process by SCA?  The SCA BPEL spec talks about the way in which

serviceReferences are supplied in a variable typed as a serviceReferenceList for multi-valued references.

There is no such equivalent for 0..1 references.

Even if the partnerLink is not marked with @initializePartnerRole at all, it is STILL possible for the partnerLink to

be uninitialized and so unusable without being assigned a value by the BPEL process - this is the result of that

"MAY" in the BPEL 2.0 spec, listed above.  Again, there is no means by which the BPEL process can get a

serviceReference to assign into the partnerLink.

B) If the partnerLink IS initialized, how can the BPEL process determine the difference between the case where the

reference is wired and the case where the reference is unwired?

There is no standard means for doing this in BPEL.

So, I think we may have a problem with 0..1 references in the SCA BPEL spec.



Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431  
Email:  mike_edwards@uk.ibm.com

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