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Re: Rationale for Dropping the <soap:body use=...> Attribute

From: <ryman@ca.ibm.com>
Date: Wed, 18 Sep 2002 13:35:44 -0400
To: Jacek Kopecky <jacek@systinet.com>
Cc: WS Description WG <www-ws-desc@w3.org>
Message-ID: <OF8EDAA596.C7E51ACE-ON85256C38.005BD195@torolab.ibm.com>


I think it's useful to seperate the discussion into two parts:

1) abstract (binding neutral) definition of messages in WSDL
2) format of messages in the SOAP binding

Concerning 1) I am in favour of just using XML schema. In fact, there is
also discussion that the <message> element be removed and that messages be
directly defined using schema, i.e. without <part>s. Allowing different
schema languages is a step in the opposite direction.

Concerning 2) the WS-I.org recommendation is to just use literal. Also,
WS-I.org is working on an algorithm to encode graphs in a way that can be
described using a literal schema. So if the concrete message format is XML,
then I see little benefit in allowing the concrete schema to be different
than the abstract schema. However, there are important cases where the
concrete message format is not XML. For example, in HTTP GET the input
parameters are url encoded. (e.g. the input gets encoded as symbol=IBM and
not as <symbol>IBM</symbol>). Also, if the message includes binary
resources, then we can describe them abstractly as some restriction of
xsd:hexBinary, but the concrete message format could be a MIME type such as
image/jpeg using SOAP with attachments.

To summarize:
- First, we should view the message definition as abstract and use XML
Schema as the abstract data type language. This establishes a proper
layering in WSDL by isolating the message definition from the bindings.
-Second, we should define the concrete message format in the binding.
-Third, evidence from WS-I.org tells us that for the SOAP binding, we can
live with literal only for concrete XML messages.
-Fourth, using literal only doesn't mean that the abstract message
definition is always concrete since there are other important non-XML
formats such as url encoding and MIME.

Arthur Ryman

                      Jacek Kopecky                                                                                                                 
                      <jacek@systinet.c        To:       Arthur Ryman/Toronto/IBM@IBMCA                                                             
                      om>                      cc:       WS Description WG <www-ws-desc@w3.org>                                                     
                                               Subject:  Re: Rationale for Dropping the <soap:body use=...> Attribute                               
                      09/18/2002 12:11                                                                                                              

 if you want an abstract schema at the wsdl:message level, that's OK
with me and it's understandable. On the other hand, if you want to
remove the use attribute by saying that "literal XML Schema" is the only
possible way in SOAP, I disagree because that either results in ugly
*and* ambiguous data structure schemata or in disallowing other data
models altogether (with SOAP Data Model among them).
 I think that especially because the parts of wsdl:message should be
described abstractly, we may need different data models right here,
otherwise we'll say that, abstractly, WSDL only describes services that
can transfer trees with very raw untyped references.
 So, either let's keep use="encoded" or let's allow different schema
languages (other than XML Schema), and I prefer the latter because it
agrees with the requirement "abstract description of wsdl:message
 Best regards,

                   Jacek Kopecky

                   Senior Architect, Systinet Corporation
Received on Wednesday, 18 September 2002 13:36:22 UTC

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