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RE: The requirements on message 'correllation'

From: Cummins, Fred A <fred.cummins@eds.com>
Date: Wed, 3 Sep 2003 15:28:26 -0500
Message-ID: <1A254DC4B97D8C4CB4A5611CF8058F5F01E93B8A@USPLM214>
To: jdart@tibco.com, "Fletcher, Tony" <Tony.Fletcher@choreology.com>
Cc: public-ws-chor@w3.org

I believe that specification of correlation in the 
choreography does not matter as long as the exchange is 
between two participants--the choreography describes
a single thread of exchanges.  I think it may matter when 
the choreography is a composite of concurrent 
exchanges between multiple participants and there
must be a definition of correlation between the binary
exchanges.  This correlation, however, may only be
required to link the specifications and might be
independent of the correlation mechanism in the
run-time messages.

Fred

> -----Original Message-----
> From: Jon Dart [mailto:jdart@tibco.com]
> Sent: Wednesday, September 03, 2003 1:43 PM
> To: Fletcher, Tony
> Cc: public-ws-chor@w3.org
> Subject: Re: The requirements on message 'correllation'
> 
> 
> 
> Fletcher, Tony wrote:
> > But picking up an argument that I think it was Frank made, 
> it may often be the case that the systems are not 
> programmatically aware that they are following a choreography 
> instance.  Suppose that a description of choreography is 
> agreed amongst some cooperating parties using our CDL.  Each 
> party then implements using BPEL as an intermediate step (or 
> directly using a programming language).  When this 
> choreography is followed the systems are in fact following an 
> unfolding instance of the choreography, but they are also 
> following an unfolding instance of interacting BPEL instances 
> (or programme instances) and it is these that the messages 
> will need to directly identify and target.
> 
> A point briefly made in the conf call was that what we are 
> building (the 
> CDL) possibly isn't really describing the implementation 
> layer through 
> which messages are actually interchanged. If it's at a sufficiently 
> abstract level, then it doesn't matter how correlation is 
> accomplished.
> 
> Now, I understand that it is also envisioned to have a binding 
> technology through which the choreography can be associated with 
> specific message formats. But again, the question is, do you need to 
> specify how correlation is accomplished at the CDL level. Or is the 
> binding still abstract in this sense?
> 
> If the participants are using BPEL as their implementation, then they 
> have a correlation mechanism available
> (http://www-106.ibm.com/developerworks/library/ws-bpel/#messag
ecorrelation).

If they're using something else, then they likely need a corresponding 
standard.

However, the issue then is, do we need to specify what that is? Or in 
fact, as Yaron was saying, do we actively not want to specify the 
correlation mechanism, to avoid precluding use of existing/emerging 
standards?

I understand the concern about interop but if we are not going to the 
level of laying out the full semantics of the implemenation (as BPEL 
does) then interop isn't really an issue, it seems to me.

Btw. I am not sure punting this issue to WSA is going to really help. 
The WSA doc says right at the start that "The architecture does not 
attempt to specify how Web services are implemented, and imposes no 
restriction on how services might be combined". Which is not to say they 
can't discuss the issue, but specifying an implementation is not in 
scope for them (IMO).

--Jon
Received on Wednesday, 3 September 2003 16:29:16 GMT

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