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RE: Importing schemata into WSDL

From: Jacek Kopecky <jacek@systinet.com>
Date: 21 Oct 2002 11:59:03 +0200
To: Don Mullen <donmullen@tibco.com>
Cc: "'Sanjiva Weerawarana'" <sanjiva@watson.ibm.com>, WS Description WG <www-ws-desc@w3.org>
Message-Id: <1035194343.18023.120.camel@krava>

Don, please see inline. 8-)


                   Jacek Kopecky

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


> 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.

I see what you meant. It's true that non-WSDL schema tools may have
problems with interpreting inline schemata, but I think the idea is that
such tools would be used by WSDL tools.

> 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.

I don't know the current developments, but in my days the solution was
to assume that two types (or elements) with the same identification
(QName) are defined equally - that's the idea behind namespaces anyway,
isn't it? 8-) So I'd never parse a definition for a known QName again. I
recognize the world is not ideal, but my response to those who want to
use schemata with different definitions for same identifiers would be
basically "go correct the schemata". 8-)

> 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.

Don, in the previous message the analogy was different - WSDL including
XSLT, not XSLT including Schema. I disagree we don't have to include
schemata inside WSDL - a good self-contained WSDL document is much
easier to distribute to places where access to external resources is
limited. Say for example we want to include a WSDL in the text of a
program (so that it can be distributed as a single binary) - we would
have to add some kind of in-memory filesystem support or file-access
redirection if external schemata were imported in this WSDL.

> 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.

Auto manufacturers sell cars with a pre-bundled spare tire instead of
just giving you the phone-number to call when you need one, because you
(all too often) need the tire. 8-)

> 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. 

Possible, out of my personal experience. 8-)

> 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.

I'm not sure if it really is the best practice. Does WS-I say anything
on this topic? They come from practice so if they don't require (or at
least suggest) that schemas be external (or internal), it doesn't seem
to be such an issue.

Jacek
Received on Monday, 21 October 2002 06:06:31 GMT

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