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Re: Issues with XML schema

From: Jacek Kopecky <jacek@systinet.com>
Date: 21 May 2003 14:20:15 +0200
To: Roberto Chinnici <Roberto.Chinnici@Sun.COM>
Cc: WS-Description WG <www-ws-desc@w3.org>
Message-Id: <1053519615.6139.18.camel@localhost>

Roberto, 

I think I see the issue with IDs and IDREFs, but are you proposing that
WSDL would require that XML Schema used for describing the blocks in
messages must not use these types?

I think that while these problems surely exist as described, they are
solvable with the proper support from the infrastructure and we
shouldn't go forbidding the ID and IDREF types. We can note the issue
somewhere and let the implementations deal with it.

Best regards,

                   Jacek Kopecky

                   Senior Architect
                   Systinet Corporation
                   http://www.systinet.com/





On Thu, 2003-05-08 at 00:02, Roberto Chinnici wrote:
> I had an action item to explain some of the issues with XML Schema that could 
> lead to subsetting it in the Web services space.
> 
> The basic problem I see is that SOAP is an enveloping technology for blocks 
> which are meant to be processed independently. But XML Schema (and XML itself, 
> e.g. with ID/IDREF) allows one to specify constraints whose validation rules 
> are applied across the whole document.
> 
> So, for instance, an application that generates a XML fragment that will 
> become a block in a SOAP envelope must take same care when specifying the 
> value for an attribute of type xsd:ID, as a poor choice would result in an 
> invalid *envelope*. Notice that if the fragment was considered in isolation, 
> i.e. as a mini-document, it would be valid. Where it gets tricky is that, in 
> order to make sure that the resulting document is valid, the application must 
> have full knowledge of the schemas for *all* the blocks (because any attribute 
>   could be an ID).
> 
> The converse, a fragment that is invalid in isolation but becomes valid in the 
> context of a larger document, can be readily demonstrated using an attribute 
> of type xsd:IDREF whose value doesn't match any IDs in the fragment.
> 
> Initially I thought the same problem would apply to identity constraints in 
> schema, but now that I found out that the XPath expressions in the 
> <xsd:selector/> element must use the "child" axis I don't think that's the 
> case. In other words, these constraints always operate within a fragment.
> 
> Hopefully some of the schema gurus on this list will jump in and confirm or 
> reject my conclusions...  ;-)
> 
> Roberto
Received on Wednesday, 21 May 2003 08:20:25 GMT

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