Re: [wsbpel] Issue - 120 - What are the semantics when an initial<receive> has no correlation set?

["Yaron Y. Goland" <ygoland@bea.com>]

It occurs to me that we can break this problem down a little more.

One can trivially imagine a web service that consists of exactly one 
request/response pair that receives a message, processes it, sends a 
response and exits. Such a webservice would have no need to use 
correlation sets. Therefore I think we can be sure that at a minimum we 
want to make it possible to define a BPEL that has a single start 
activity with no correlation set that doesn't create a singleton.

What this argues to me is that the default interpretation of a BPEL with 
a start activity with no correlation set is that it is not a singleton.

Therefore what 120 really should be about is - do we want to 
intentionally add an attribute or other mechanism to specify that a BPEL 
process is intended to be a singleton?

We already know we can simulate a singleton in BPEL by having an 
instance with a start activity that is only known to the deployment 
environment and then having all subsequent messages sent to the single 
BPEL instance. But I readily admit that this is a less than clean 
solution. It is best when possible to directly express one's semantics.

So I think we can then rephrase the issue once again to - Is it worth 
defining explicit singleton behavior in BPEL 2.0 (or whatever we call it)?

To which, given our other priorities, I think the answer is no. But I 
realize that my answer is just a matter of opinion.

	Just my two cents,

		Yaron

Ugo Corda wrote:

> 
> I think the term "semantics" was used here primarily to refer to the 
> expected behavior in case a second message is sent to the same <receive> 
> at the time an instance is already active (see Issue 118 discussions). 
> Should the second message be understood as creating a new instance, or 
> should it be seen as a message sent to a singleton instance 
> (and therefore dropped since the corresponding <receive> is not active 
> at that time)? As I remember from the issue 118 discussions, use cases 
> can be made for both interpretations.
>  
> Ugo
> 
>     -----Original Message-----
>     *From:* Ron Ten-Hove [mailto:Ronald.Ten-Hove@Sun.COM]
>     *Sent:* Thursday, August 12, 2004 11:16 AM
>     *To:* wsbpel@lists.oasis-open.org
>     *Subject:* Re: [wsbpel] Issue - 120 - What are the semantics when an
>     initial <receive> has no correlation set?
> 
>     It seems to me that we can't actually read too much into the fact
>     that an initiating <receive> activity doesn't initiate a correlation
>     set at the same time. Two possibilities come to mind:
> 
>         * The process is actually very simple, and doesn't need
>           correlation (ie, it has no other <receive> activities).
>         * The process initiates the correlation set in a later <invoke>
>           activity. 
> 
>     So it seems that it would be inappropriate to infer any special
>     semantics to the <receive> in question.
> 
>     -Ron
> 
>     ws-bpel issues list editor wrote:
> 
>>     This issue has been added to the wsbpel issue list. The issues
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>>
>>         Issue - 120 - What are the semantics when an initial <receive>
>>         has no correlation set?
>>
>>     *Status:* open
>>     *Categories:* Correlation <#category_correlation>
>>     *Date added:* 19 Apr 2004
>>     *Submitter:* Danny van der Rijn <mailto:dannyv@tibco.com>
>>     *Date submitted:* 19 April 2004
>>     *Description:* when an initial <receive> has no correlation set
>>     should the instance be singleton, or be allowed to have multiple
>>     instances outstanding in parallel?
>>     *Changes:* 19 Apr 2004 - new issue
>>
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