RE: XML Schemas: Best Practices ? Versioning

[Michael Brennan <Michael_Brennan@allegis.com>]

My reference to your conversations with W3C folks as "irrelevant" was
probably too abrasive. I hope you didn't read any insult into that. What I
should have said is that such conversations are only relevant to the degree
they help clarify thinking or motivation behind something in the spec. If
such conversations convey thinking that is inconsistent with the spec, that
has to be disregarded. It is the spec that must be regarded as
authoritative.

> From: Michael Brennan [mailto:Michael_Brennan@allegis.com]
> Sent: Friday, September 07, 2001 1:02 PM
> To: 'Tony.Coates@reuters.com'; xml-dev@lists.xml.org
> Subject: RE: XML Schemas: Best Practices ? Versioning
> 
> 
> > From: Tony.Coates@reuters.com [mailto:Tony.Coates@reuters.com]
> 
> <snip/>
>  
> > Once again, too much emphasis on the belief that everything 
> > should work even if there is no "schemaLocation" given.  I 
> > really believe that taking this view, which does not seem to 
> > be the view of the W3C people I've talked to, will just lead 
> > to more complication than is necessary.
> 
> I strongly disagree with this. Building a distributed web 
> architecture that
> relies upon explicit specification of system paths to schemas 
> in instance
> documents that may be exchanged among parties over the 
> internet leads to
> more complication than is necessary. This approach is fraught 
> with problems.
> Quite apart from that, private conversations you have had 
> with W3C people
> are irrelevant. Implementors of schema processors have to 
> rely upon the
> published specifications. They cannot take into account private
> conversations to which they are not privy. I have serious 
> problems with
> people claiming that private conversations with W3C members 
> are somehow more
> authoritative than the published specifications. 
> 
> The XML Schema specifications are quite explicit on this matter. The
> schemaLocation attribute is optional. Quite apart from that, 
> it is only a
> hint to help a processor to locate the schema. It is not 
> authoritative even
> if it is present. That is quite clearly stated in the section 
> on "how schema
> definitions are located on the web"
> (http://www.w3.org/TR/xmlschema-1/#schema-loc). To suggest that it is
> appropriate to keep the same namespace URI, but change 
> schemaLocation when a
> schema changes strikes me as a an extremely poorly thought 
> out bad practice.
> It is the namespace URI that is authoritative, here; not the 
> schemaLocation
> hint. XML Schema's discussion of names and symbol spaces
> (http://www.w3.org/TR/xmlschema-1/#concepts-nameSymbolSpaces) 
> make that
> quite clear. In terms of XML Schema, a namespace is a symbol 
> space. Reusing
> the same namespace URI for multiple symbol spaces seems to me 
> to clearly
> violate the intent of XML Schema's use of namespaces. I would 
> regard the
> practice of reusing the same namespace URI for different schemas, and
> differentiating between them in instance documents purely by the
> schemaLocation attribute, to be an extremely bad practice.