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Subject: Re: [wsbpel] Issue - 118 - When are Correlation Sets Mandatory?


Far from there being anything wrong with the case you describe, it is, 
in fact, quite common and even has a name - a singleton service.

But couldn't one trivially implement a singleton service by creating a 
BPEL with a single start activity which is access restricted so that 
only the admin can call it? The admin would then call the start activity 
exactly one time. That would guarantee that there was only one instance 
of the service.

I admit that it would be nice to have a way to mark a service as a 
'singleton' but given that there is a work around I'm not sure it's 
worth providing a dedicated short cut.

		Yaron

Ugo Corda wrote:

> 
> Hmm, this requirement for correlation sets sounds surprising to me too. 
> I would have thought that, when a process is instantiated that does not 
> have a correlation set defined, a single instance of that process would 
> exist. All messages would be sent to that single instance. No new 
> instances would be created until that existing instance terminates. I 
> don't fully understand what would be wrong with the scenario I just 
> described.
>  
> Ugo
> 
>     -----Original Message-----
>     *From:* ws-bpel issues list editor
>     [mailto:peter.furniss@choreology.com]
>     *Sent:* Thursday, April 15, 2004 10:58 AM
>     *To:* wsbpel@lists.oasis-open.org
>     *Subject:* [wsbpel] Issue - 118 - When are Correlation Sets Mandatory?
> 
>     This issue has been added to the wsbpel issue list. The issues list
>     is posted as a Technical Committee document to the OASIS WSBPEL TC
>     pages <http://www.oasis-open.org/apps/org/workgroup/wsbpel> on a
>     regular basis. The current edition, as a TC document, is the most
>     recent document with the title **in the "Issues" folder of the
>     WSBPEL TC document list
>     <http://www.oasis-open.org/apps/org/workgroup/wsbpel/documents.php>
>     - the next posting will include this issue. The list editor's
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>     announced, is available at this constant URL
>     <http://www.choreology.com/external/WS_BPEL_issues_list.html>.
> 
> 
>         Issue - 118 - When are Correlation Sets Mandatory?
> 
>     *Status:* open
>     *Categories:* Correlation
>     *Date added:* 15 Apr 2004
>     *Submitter:* Yaron Y. Goland <mailto:ygoland@bea.com>
>     *Date submitted:* 15 April 2004
>     *Document:* BPEL Specification
>     *Description:* It wasn't until Satish explicitly pointed it out to
>     me that I finally understood that all Picks and Receives MUST have
>     at least one correlation set defined on them with "initiate = 'no'"
>     unless the pick/receive is a start activity. I had always assumed
>     that the system was allowed to implicitly route messages based on
>     URL but that is in fact wrong. All routing criteria MUST be explicit
>     and MUST be specified by a correlation set. This also means that it
>     is always illegal to have a pick or receive which does not have at
>     least one correlation set on it.
> 
>     Normative Change - The schemas for pick and receive make correlation
>     sets optional. That would appear to be wrong.
> 
>     Also, I'm unclear about what assumptions we make regarding invoke,
>     specifically, is there a requirement to have a correlation set
>     defined on pattern="in" on an invoke? This is kind of a tricky
>     issue. If a synchronous transport is being used then there may not
>     be any explicit information available to mark the response for
>     correlation purposes. In that case do we allow the correlation set
>     for the response to be left off or do we require programmers to use
>     issue 96 : Engine-managed correlation sets <#Issue96>?
> 
>     Also note, that the WSDL 1.1 spec quite clearly states that
>     request/responses do not have to be sent over synchronous transports
>     so there may be values we could use for correlation sets. In other
>     words, the situation is inconsistent. In some cases a
>     request/response uses a synchronous transport and in other cases it
>     could be using an asynchronous transport with some message based
>     correlation. Do we want to distinguish these cases or do we want to
>     just say that we presume that any time a request/response pattern is
>     used there is some correlation mechanism implicitly known to the
>     engine and therefore correlation sets are always optional on the
>     incoming message? Reply has the same issue as responses on invokes.
>     *Changes:* 15 Apr 2004 - new issue
> 
>     To comment on this issue, please follow-up to this announcement on
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> 


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