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Re: Question About Namespaces and DTDs

• From: "Simon St.Laurent" <simonstl@s...>
• To: "Winchel 'Todd' Vincent, III" <winchel@m...>,xml-dev@l...
• Date: Tue, 25 Jul 2000 08:56:17 -0400

At 12:13 AM 7/25/00 -0400, Winchel 'Todd' Vincent, III wrote:
>Based on what St. Laurent wrote, it seems to me, at first blush, that this
>could be solved by requiring unique namespaces prefixes.  Am I missing
>something?  I realize the W3C is not going down this path.  However, I'm
>wondering . . . if I were trying to build a global architecture for a
>variety of documents that exist within the same industry, wanting each of
>those document types to exist in a different namespace (within the industry
>architecture) and be able to mix using namespaces, could I not simply
>require all applications conforming to that particular industry standard to
>use unique prefixes.

To some extent - the extent to which vocabulary designers control usage -
this is possible.  

In the Common XML spec (http://simonstl.com/articles/cxmlspec.txt),
basically a list of ways to use XML and Namespaces as safely as possible,
we recommend such an approach on a document-by-document basis.  Avoid
prefix clashes, and the complexities of namespace processing disappear.  

To the extent that you can control prefixes, you can also use DTDs
reliably.  It turns out there are also some amazingly obfuscated ways of
creating DTDs that can survive prefix changes, though I don't think they
(easily, anyway) let you change between the default namespace (no prefix)
and prefixed namespaces.

>A further thought . . . to be manageable, it seems to me that this would
>require a registry of prefixes for the particular industry.   Assuming a
>registry were possible, would namespaces and DTDs mix?

They could, but I think some folks at the W3C would be aghast at the
suggestion that URIs weren't the right answer.  I don't think you'd be able
to find enough support to implement such a thing, especially as there
aren't yet enough namespaces in the world for clashes to be causing
large-scale and regular problems.

>My apologies if this is a simple question.  I'm trying to get my head around
>it and would appreciate any pointers to resources that will provide
>clarification.

None of these are simple questions, except in the simplest of situations.
I've included a few pointers below where you might find more answers, or at
least more questions.

http://www.xmlhack.com/list.php?cat=7 - Namespaces news

http://www.xml.com/pub/2000/03/08/namespaces/index.html - Ron Bourret's
"Namespace Myths Exploded"

http://www.jclark.com/xml/xmlns.htm - James Clark on namespaces

http://lists.w3.org/Archives/Public/xml-uri/2000May/0227.html - Pointers to
prior mostly URI-focused namespace discussions 

http://www.xml.org/archives/xml-dev/2000/04/thread.html#397 - Thread on
using parameter entities for namespace prefixes

There are a few thousand other messages I could point to, but those are
likely the high points.

Simon St.Laurent
XML Elements of Style / XML: A Primer, 2nd Ed.
http://www.simonstl.com - XML essays and books

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