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RE: MEP proposal

From: Martin Gudgin <mgudgin@microsoft.com>
Date: Fri, 21 Feb 2003 08:06:32 -0800
Message-ID: <92456F6B84D1324C943905BEEAE0278E02D30D0F@RED-MSG-10.redmond.corp.microsoft.com>
To: "Amelia A. Lewis" <alewis@tibco.com>, "Jacek Kopecky" <jacek@systinet.com>
Cc: "Jeffrey Schlimmer" <jeffsch@windows.microsoft.com>, <www-ws-desc@w3.org>



> -----Original Message-----
> From: Amelia A. Lewis [mailto:alewis@tibco.com] 
> Sent: 21 February 2003 15:58
> To: Jacek Kopecky
> Cc: Martin Gudgin; Jeffrey Schlimmer; www-ws-desc@w3.org
> Subject: Re: MEP proposal
> 
> 
> 
> 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.

That was my understanding too.

> 
> > 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.

Agreed.

> 
> 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?

I think that the bindings will describe the relationship between, for
example, the SOAP Request/Response MEP and a given MEP for a WSDL
operation.

> 
> > 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.

And I see no reason why it should do so. The WSDL says, in order to talk
to me, this is what you need to know. You could use that info to write
client code that can talk to the service, or you can use that info to
write intermediary code to talk to the service. Either way, the service
doesn't know, and doesn't care, which of those you did.

> 
> 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.

Agreed.

Gudge
Received on Friday, 21 February 2003 11:07:05 GMT

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