RE: Resources and URIs

> > Can you sketch out a situation where someone thinking every URI
> > had a denotation would build software that did the wrong thing?  
> 
> The most widely deployed system today which uses URIs for
> denoting something other than the resource identified is
> the XML namespace system. 

No. Sorry. I disagree.

URIs used as XML Namespaces do *not* denote those namespaces.

XML Namespaces are punctuation. They are macros. They are
syntactic sugar for XML instances so that URIs can be
used as element and attribute names (by a little bit of
slight of hand).

Using a URI as an XML Namespace does not, in any way, affect
the denotation of that URI nor tie the denotation of the URI
to any XML Namespace related semantics.

Nor does the URI used as an XML Namespace need to have any
semantic relationship to any of the URIs grounded in that
namespace.

If it happens to be the case that the URI used as an XML
Namespace happens to denote a vocabulary and the URIs
grounded in that namespace happen to denote terms of that
vocabulary, that is purely a matter of coincidence or
at best, convenience to the author of that vocabulary.

> In some circumstances, a
> URI such as "http://www.w3.org/1999/xhtml" is used to
> denote 'the contents of that web page at the exact
> instance it was uttered'. If I believed that, then
> when I saw xmlns="http://www.w3.org/1999/xhtml" in
> some XML instance, I would need to find out the creation
> date of the XML instance and go to 
> http://web.archive.org/web/*/http://www.w3.org/1999/xhtml
> to see that there have been at least three versions
> of http://www.w3.org/1999/xhtml, and I might have
> to build a model of XML namespaces where namespaces
> changed over time.

No. You wouldn't have to concern yourself at all with whatever
might be denoted by the URI used as a namespace name. That
is irrelevant. Only the complete terms based on the namespace
name and the local name are relevant to the XML application.

The XML namespace name is just punctuation of the XML serialization.

> I can have a conversation with you about the history
> of 'http://www.w3.org/1999/xhtml' as a web page maintained
> by the W3C webmaster (in RCS, no less, currently saying
> Last modified: $Date: 2003/04/11 14:00:50 $) and another
> conversation with you about the XHTML namespace.
> The two concepts are different. Which is the (single?)
> denotation of the URI?

Firstly, when you say "XHTML namespace" I am taking that to
mean the XHTML vocabulary, not an XML Namespace name used to
ground URIs denoting terms of that vocabulary. 

Given that:

1. I would presume (and possibly be wrong, since the owners of the URI 
   in question don't explicitly say themselves) that http://www.w3.org/1999/xhtml 
   denotes the XHTML vocabulary.

   Sending a GET request to the HTTP server accessible at www.w3.org
   may return a representation of the XHTML vocabulary that is a web page,
   but that does not mean that the URI actually denotes that web page.

   The URI denoting the web page representation itself is probably
   http://www.w3.org/1999/xhtml.html.

2. http://www.w3.org/1999/xhtml is also used as as an XML Namespace
   name by various XML instances and XML schemas to facilitate the
   use of XHTML terms as element and attribute names.

3. The definition of the semantics of the terms of the XHTML vocabulary
   have changed over time, even if the URIs denoting those terms and
   the XML Namespace name have themselves not changed.

4. Even though the URI used as the XML Namespace name in conjunction with
   various XML instances referring to the terms of the XHTML vocabulary
   likely does denote the XHTML vocabulary itself, it could also have
   just as well denoted a jelly donut on my desk and some other URI could
   be used to denote the vocabulary. The fact that the URI used as the
   XML Namespace name does in fact denote the vocabulary is simply a
   practical convenience, not a technical requirement.

5. Any RDF statements using http://www.w3.org/1999/xhtml as the subject
   describe the XHTML vocabulary.

6. Any RDF statements using http://www.w3.org/1999/xhtml.html as the subject
   describe the web page.

Patrick

--
Patrick Stickler, Nokia/Finland, (+358 40) 801 9690, patrick.stickler@nokia.com

Received on Wednesday, 7 May 2003 04:39:13 UTC