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Re: section 2.2.22 Message Exchange Pattern (MEP)

From: David Booth <dbooth@w3.org>
Date: Thu, 10 Jul 2003 18:14:21 -0400
Message-Id: <5.1.0.14.2.20030710170250.02aace98@localhost>
To: jones@research.att.com, Christopher B Ferris <chrisfer@us.ibm.com>
Cc: www-ws-arch@w3.org

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 Thursday, 10 July 2003 18:23:35 GMT

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