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

[Mike Edwards <mike_edwards@uk.ibm.com>]

Raiser:        
       Mike Edwards

Target:        
       

Description:

 
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. 

Proposal:

None


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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