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   Re: Irony heaped on irony

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  • From: David Carlisle <davidc@nag.co.uk>
  • To: timbl@w3.org
  • Date: Sat, 20 May 2000 23:36:39 +0100 (BST)

   ...or presumably (4)  the schema document returned on a query of the
   namespace URI
    contains some information in xml-schema and some in rdf-schema.  (and some
   in XHTML for people?)

   Isn't this what multiple namespaces in a document can be used for?


I don't understand the last comment, could you expand on it?

I can't see how you can use multiple namespaces in a document to return
different sorts of information about a given element.
Each element is only in one namespace.

It seems all your use cases involve locating a schema (of some sort)
at the namespace URI. This will of necessity be such a rare and marginal
case that it is a dangerous thing to use as a basis for changing the
namespace rec.

It only makes sense to use the namespace URI as the schemaLocation if
there is a direct 1-1 correspondence between the namespace and schema.

This will almost never be the case, Just consider the current W3C
namespaces as examples,

XHTML one namespace 5 schema (xhtml 1.0 strict, transitional, frameset,
xhtml basic, xhtml 1.1) and we're still in the first year.

MathML one namespace 2 schema (mathml 1 predated namespace rec but the
MathML namespace is dated 1998 and effectively added to MathML 1 once
announced, and the later MathML 2 drafts use the same namespace.

XSLT one namespace, currently just xslt 1.0, but xslt rec explicit how
versioning of future versions will go, and they will be in the same
namespace, but would of course require different schema.

For historical reasons most of the current schema are in dtd syntax,
but there is no reason to suppose things will be different once we
switch to xml schema syntax. There will usually be several schema
for any given namespace.

If in the early days of a schema for version 1.0 of a language you make
large scale use of the  shortcut of using the namespace URI to avoid
writing schemaLocation, you will just be storing up confusion for users
when version 2 inevitably comes out. You can't change the namespace but
you need to put the schema at a different URI, so in the end you have to
use schemaLocation anyway.


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