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Re: MEP proposal

From: Amelia A. Lewis <alewis@tibco.com>
Date: Fri, 21 Feb 2003 10:58:27 -0500
To: Jacek Kopecky <jacek@systinet.com>
Cc: mgudgin@microsoft.com, jeffsch@windows.microsoft.com, www-ws-desc@w3.org
Message-Id: <20030221105827.3fe8b646.alewis@tibco.com>

Dear Jacek,

Thanks for the comments.

On 21 Feb 2003 16:41:36 +0100
Jacek Kopecky <jacek@systinet.com> wrote:
> I think it's the good direction. I do have comments/questions:
> 
> The MEPs say nothing about where the 'in' messages come from or where
> the 'out' messages go to, which may be confusing. Although I first
> thought it's OK, the MEP8 below suggests otherwise. Without the comments
> specifying the sources/destinations, the MEP would be extremely abstract
> and confusing.

Well, I had understood that the Scottsdale face-to-face ruled out modeling of intermediaries in MEPs, or more than two node roles.  If so, then MEP8 won't fly, since it's both.

> Who will specify (and where will that be) the relationships between SOAP
> MEPs, possible abstract MEPs (if anyone comes up with such beasts) and
> WSDL MEPs?

I thought that we *were* defining abstract MEPs, here.

If so, then the architecture would presumably call for SOAP MEPs to be defined with reference to the abstract MEPs, and likewise the WSDL MEPs would refer to either SOAP or abstract MEPs.  The WSDL MEPs might be no more than "this is how this particular abstraction is represented syntactically."

But I might not be fully in synch with Gudge and Jeff on that one.  Guys?

> For example, SOAP Request/Response maps to MEP2, SOAP
> Response maps either to MEP4 or MEP2, and 

Right, presumably if there were abstract MEPs, then the MEPs that SOAP references would specify which.

> a potential SOAP Req/Resp MEP
> involving one intermediary would map to two WSDL MEPs - MEP2 for the
> service and MEP8 (below) for the intermediary.

I thought that this was out of scope.  Intermediaries, in particular, are severely problematic to model, since SOAP has a bit of a split personality about whether they are visible or not.  At present, insofar as I am aware, WSDL does not attempt to model any information about intermediaries, at all.

So, in WSDL, if the intermediary were visible, it would be a service, and the fact that it mediated between a particular service and its clients wouldn't be visible.  It would expose a MEP2; the fact that it is (behind the scenes) using a MEP2 on the "real" service (with itself in a client/forwarding role) isn't visible in the WSDL.

Or such is my understanding.

> And that's not
> considering describing the client in a WSDL. 8-)

Yes, but we haven't developed a web CLIENT description language.  If it isn't a service, it isn't our problem, is it?  Except insofar as the SERVICE description should be adequate to allow a client to actually use the service.

Amy!
-- 
Amelia A. Lewis
Architect, TIBCO/Extensibility, Inc.
alewis@tibco.com
Received on Friday, 21 February 2003 10:58:18 GMT

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