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RE: section 2.2.22 Message Exchange Pattern (MEP)

From: Cutler, Roger (RogerCutler) <RogerCutler@chevrontexaco.com>
Date: Fri, 11 Jul 2003 09:16:09 -0500
Message-ID: <7FCB5A9F010AAE419A79A54B44F3718E025D866B@bocnte2k3.boc.chevrontexaco.net>
To: "David Booth" <dbooth@w3.org>, jones@research.att.com, "Christopher B Ferris" <chrisfer@us.ibm.com>
cc: www-ws-arch@w3.org

Is then, in reality, an MEP a choreographic exchange pattern that is on
a list of patterns that people find particularly important?

-----Original Message-----
From: David Booth [mailto:dbooth@w3.org] 
Sent: Thursday, July 10, 2003 5:14 PM
To: jones@research.att.com; Christopher B Ferris
Cc: www-ws-arch@w3.org
Subject: Re: section 2.2.22 Message Exchange Pattern (MEP)



At 10:49 AM 7/10/2003 -0400, jones@research.att.com wrote:
>  2.2.22.1 Summary
>  A message exchange pattern is a template for the exchange of messages
>  between agents that arise from a message and its responses, if any.

I don't think the definition of MEP should be restricted this way.   The

addition of the phrase "that arise from a message and its responses, if 
any" makes this definition unnecessarily restrictive.  In fact, this 
defintion is not even consistent with either WSDL 1.2 or SOAP 1.2 today!

For example, in WSDL 1.2, the "Multicast Solicit Response"[1] pattern
may 
involve a sequence of THREE messages: (1) the initial "solicit" message;

(2) the normal response message; and (3) a fault message that is
returned 
as a result of the response message.

And in SOAP 1.2, the SOAP 1.2 definition of MEP does not restrict the 
concept of MEPs to only those patterns that "arise from a message and
its 
responses".  In fact, the SOAP 1.2 definition of MEP does not restrict 
either the number of messages or the number of nodes involved.

I think it makes more sense for our WS Architecture to define MEP more 
broadly, and recognize that MEPs may range from simple to complex.  Some

languages, such as WSDL, may only deal with simple MEPs involving only 
sequences of one, two or a few messages or nodes (such as request or 
response).  Others, such as choreography, may permit very complex MEPs
to 
be described (presumably out of simpler building blocks).  Both WSDL and

SOAP define certain, specific MEPs, (and clearly the relationship
between 
them should be clear), but these are only a few of the possible universe
of 
all "Message Exchange Patterns".

I propose simplifying our definition of "Message Exchange Pattern" to:

"2.2.22.1 Summary
  A message exchange pattern is a template for the exchange of messages
  between agents."

1. 
http://dev.w3.org/cvsweb/~checkout~/2002/ws/desc/wsdl12/wsdl12-patterns.
xml#multicast-solicit-response
2. http://www.w3.org/TR/2003/PR-soap12-part1-20030507/#soapmep


-- 
David Booth
W3C Fellow / Hewlett-Packard
Telephone: +1.617.253.1273
Received on Friday, 11 July 2003 10:18:17 GMT

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