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RE: Importing schemata into WSDL

From: VAMBENEPE,WILLIAM (HP-Cupertino,ex1) <william_vambenepe@hp.com>
Date: Thu, 17 Oct 2002 19:15:43 -0400
Message-ID: <155C6BB395577C4EA8F65A9ADA9F2104DA8BFA@xcup01.cup.hp.com>
To: WS Description WG <www-ws-desc@w3.org>


> Don> It seems unlikely that I am going to win this argument 
> (especially
> since I've heard no one in the group support this view!).  I 
> would like to
> see some text in the spec, however, that indicates that 
> although embedded
> schemas are supported in WSDL, best practice dictates that schemas be
> imported.

+1

--
William Vambenepe
Web Services Management Operation
HP OpenView Division


> -----Original Message-----
> From: Don Mullen [mailto:donmullen@tibco.com]
> Sent: Thursday, October 17, 2002 3:26 PM
> To: 'Jacek Kopecky'
> Cc: 'Sanjiva Weerawarana'; WS Description WG
> Subject: RE: Importing schemata into WSDL
> 
> 
> 
> Jacek:
> 
> Response inline.
> 
> Don
> 
> -----Original Message-----
> From: Jacek Kopecky [mailto:jacek@systinet.com]
> Sent: Thursday, October 17, 2002 11:19 AM
> To: Don Mullen
> Cc: 'Sanjiva Weerawarana'; WS Description WG
> Subject: RE: Importing schemata into WSDL
> 
> Don,
> 
> I disagree with points 1 and 3 from my experience of having 
> implemented
> (or cooperated on) a set of WSDL tools.
> 
> Don> The problem is not WSDL tools, that obviously would be aware of
> whatever is standard for WSDL, it is compatibility with 
> non-WSDL tools that
> matters for issue #1.
> 
> Don> I would be interested in hearing how you solve issue #3.  Is your
> solution interoperable?  It seems to me the potential for 
> having two type
> definitions that claim to be the same type, a truly complete 
> tool would need
> to verify that the types are the same.  If  you don't do that, you are
> simply ignoring the problem, which, in my  mind, leaves this 
> objection on
> the table.
> 
> 4 should not be a problem because published schemas should seldom or
> never change; also many WSDL use unique namespaces so schema 
> management
> is mostly a schema replacement anyway. 8-)
> 
> Don> A good self-fulfilling prophecy here.  Since it is 
> difficult to share
> these schemas, they are not shared outside of WSDL.  Since 
> they are not
> shared outside of WSDL, we don't need to share them.  Hmmm.  
> We've been
> actively developing a schema / xml management tool for the 
> last few years.
> Schemas/WSDLs do change during the development cycle -- sometimes by
> multiple people across multiple organizations.
> 
> 6: well we want to say something about message parts. I think you have
> nothing against importing external schemata, so really the analogy to
> XSLT doesn't work because it isn't used in WSDL at all at the 
> moment. So
> I feel point 6 is pretty much void.
> 
> Don> Your argument misses the analogy.  For comparison, XSLT 
> 2.0 is adding
> validation, but they aren't talking about including schemas 
> "inline" in
> XSLT.  Of course we need to use schema to define types, but we don't
> necessary have to include them inline.
> 
> I agree completely with point 7. 8-)
> 
> Don> Great -- we're making progress! ;-)
> 
> XML syntax, especially namespaces, was explicitly designed for easy
> vocabulary combinations, and this is directly against your point 8.
> 
> Don> Just because it is possible, doesn't mean it is a good 
> idea.  Auto
> manufacturers could sell cars that come pre-bundled with four 
> spare tires,
> but that is not really useful, as you (almost always) only 
> need one spare
> tire.  Interoperability and backward compatibility is key -- embedded
> schemas don't work well with non-WSDL tools.
> 
> To conclude, I disagree with most of your points and I prefer we keep
> the ability to embed schemata (because in some applications it really
> simplifies distribution or processing) together with the ability to
> refer to external schema documents.
> 
> Don> You seem to have argued against most points by 
> indicating that they
> aren't valid issues.  I would argue that WSDL is currently 
> not being used to
> its fullest potential -- having been thus far basically 
> restricted to fairly
> simply request/response / SOAP over HTTP.  Expanding its use into the
> enterprise-wide pub/sub space raises many schema and wsdl 
> management issues
> that some people may not have encountered. 
> 
> Don> It seems unlikely that I am going to win this argument 
> (especially
> since I've heard no one in the group support this view!).  I 
> would like to
> see some text in the spec, however, that indicates that 
> although embedded
> schemas are supported in WSDL, best practice dictates that schemas be
> imported.
> 
> On Thu, 2002-10-17 at 16:50, Don Mullen wrote:
> > 
> > Sanjiva:
> > 
> > Some reasons not to include embedded schemas within WSDL files:
> > 
> > 1) Schema inclusion makes life difficult for tool builders. 
>  Although the
> > difficulties can be overcome, it is sometimes difficult to get
> interoperable
> > results with tools that don't get this right.
> > 
> > 2) No identifiable location... some XML validators will be 
> hard pressed to
> > make use of the embedded schemas without having a physical 
> location URI.
> > XML instance documents cannot reference embedded schemas via
> schemaLocation.
> > This could be dealt with using some sort of "inside of" or 
> fragment URI
> > convention, but again there isn't a clear interoperable way 
> to do this.  
> > 
> > 3) Embedding a shared (or 3rd party) schema into several 
> WSDLs, just for
> the
> > simplicity aspect, can trip up systems that expect only one 
> schema per
> > namespace... now you have to pick one, or compare them, or 
> something.
> > 
> > 4) Schema management across the organiziation becomes more 
> difficult when
> > you have schemas both in stand-alone documents and embedded 
> within WSDLs.
> > The embedded schemas would rarely be reused.
> > 
> > 5) In some sense (perhaps niave), it creates an expectation 
> that WSDL
> > defines types (is a schema language).
> > 
> > 6) If we are going to include schemas, why don't we also 
> include XSLT
> > operations, since it might be desirable to describe a 
> transformation of
> the
> > service request or result.  That is more obviously a silly idea.
> > 
> > 8) The only reason that these two were combined to begin 
> with stems from
> > both WSDL and XML Schema both being in XML syntax, and is 
> convenient in
> > simple stand-alone cases.  If, instead a non-XML metadata file was
> > referenced, everyone would know from the get-go that the 
> two needed to be
> in
> > separate files.
> > 
> > Don
> 
Received on Thursday, 17 October 2002 19:15:46 GMT

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