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Re: Is a namesapce a resource? - was: duck

From: David Carlisle <david@dcarlisle.demon.co.uk>
Date: Thu, 8 Jun 2000 12:16:59 +0100 (BST)
Message-Id: <m1300J1-000OdCC@dcarlisle.demon.co.uk>
To: GK@Dial.pipex.com
CC: xml-uri@w3.org


> Ignoring, for now, issues of relative and context-dependent URIs.  If a 
> namespace is a resource, and a namespace name is a URI:  what resource is 
> identified by that URI?  Logically, it is the namespace

"logically" is rather a contentious word to use:-)
If the method of naming namespaces is as indicated in the rec, and
clarified by the vast majority of namespace use and discussion since
then, then to name a namespace you pick a URI of any resource at all
(preferably one you control) so the answer to "what resource is
identified by that URI" is just "whatever resource whose URI was used
as the namespace name".

> But if one chooses a namespace name 
> that can also be used (directly) to retrieve some schema bound to the 
> namespace, then the resource identified by the URI ipso facto is the schema 
> document.  (Or is it?)

Some people have the mistaken belief that namespaces and schema are
effectively the same thing, so don't see that having the same URI
relate to a namespace and to a schema describing one possible language
using names from that namespace is at all strange.

Of course it isn't only a schema you might get. You might get the text
of the rec, or an add hoc html page describing some aspect of the
namespace or you might get someone's home page, or probably more
often than not you'll get nothing.

> Where now the 1:1 correspondence between URIs and resources?

It's where it always was, but the mistake in the argument was the
idea that the namespace name being the URI of some possibly existing
resource implies that the namespace is that resource.

> There is, I think, a related issue:  I had thought that content negotiation 
> might be used to select different representations of a schema associated 

How would content negotiation distinguish which of the 5 or 6 so far
published schema (dtd) for the xhtml namespace you want to use, or
which of the arbitrary many schema for the same namespace that you can
create using xhtml modularisation?

> I think a basic formal algebra of URIs and resources might help to set 
> some of these issues in place.

If there is no agreement on whether namespaces are the resources
identified by the URI used as the namespace names then I don't see how
any such algebra is going to help.

I claim http://www.dcarlisle.demon.co.uk is the URI representing
the "home page" of myself and my wife. Since I pay to have that
URI work, and I wrote the page in question, I think it is reasonable
for me to assert that that is the resource identified by that URI.

Now any namespace processor, without having read the above paragraph
has to decide what to do with

<x xmlns="http://www.dcarlisle.demon.co.uk"/>

Given the current rec and all proposed modifications of it,
the processor has no choice but to accept this as a conforming
document. The namespace of the element has name
http://www.dcarlisle.demon.co.uk.
But the resource identified by that URI has absolutely not changed.

Unlike Dan Connolly's img example where if I gave this URI to
<img it wouldn't work in a web browser, using my home page
URI as a namespace name works fully for all namespace processors
xpath xslt etc will all work quite happily with this namespace
and the fact that no one else should define behaviour for that
namespace is just excactly the reason given why URI syntax was
chosen for namespace names. So not only is using my home page
URI as a namesace name not wrong, it is essentially the canonical
example of the method of allocating myself a namespace name that no
one else should use.

Tim Berners-Lee and Dan Connolly have asserted that my doing that
is somehow wrong, but no one has ever suggested any change
that would make that wrong. Or what the namespace processor is
supposed to do to reject the document.


David
Received on Thursday, 8 June 2000 07:12:30 GMT

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