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SOAP Message Exchange Patterns and Web Service Addressing

From: Neil Hudson <nahudson@sqc.co.uk>
Date: Tue, 22 Nov 2005 05:29:31 +0000
Message-ID: <ChInugC7yqgDFwUo@sqct.demon.co.uk>
To: public-ws-addressing@w3.org


My understanding ( or possibly lack of understanding ) of the
interaction of WS-A EPRs and SOAP leads me to the following:

[1] If explicit Reply EPRs are mandated by the provider ( anonymous is
not allowed ) then this means that there will be  two separate SOAP
messages correlated at the WS-A level.

[2] If explicit Reply EPRs are options supported by the provider
(anonymous or explicit are allowed ) then the consumer has control,
through the type of EPR sent, over whether Request-Response MEP is
operated (anonymous Reply EPR ) or whether there are two separate SOAP
messages correlated at the WS-A level (explicit Reply EPR ).

The WSDL 2.0 SOAP Binding requires that SOAP MEPs are specified in the
WSDL and exist in the WSDL component model.  It appears to me that
existing predefined MEP options and the behaviour they imply do not
readily match the behaviour(s) described above.

To avoid conflict and misunderstanding would it be appropriate for the
WS Addressing SOAP binding to specify a MEP or MEPs that correspond to
the pattern of message exchanges required to comply with the WS-A EPR
semantics?  There could be a SOAP MEP identifier defined of the form:

        wsa:WsaSoapMep

that can be used in the SOAP binding MEP property of the WSDL

        wsoap:mep="wsa:WsaSoapMep"

to indicate that the sequence of SOAP message exchanges complies with
the WS-A rules rather than a standard SOAP MEP such as R-R.

The WS-A MEP could also have an alternative for use in case [1] that
mandates two messages though this may not be essential as the general
case does appear to address this.

In summary if a standard MEP were specified in the WSDL then this would
be incompatible with the EPR rules and the implementation would have to
break one set of rules.  A specific MEP could avoid this conflict and
clearly indicate to developers what is expected.

Regards

Neil

-- 
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Neil Hudson CEng MBCS MIEEE
British Computer Society Registered Consultant
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SQC Technology Limited
Phone : +44(0)1283 763632
Fax   : +44(0)1283 763631
Email : nahudson@sqc.co.uk
Web   : http://www.sqc.co.uk
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Received on Tuesday, 22 November 2005 05:30:00 GMT

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