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Re: [rdfmsQnameUriMapping-6] Algorithm for creating a URI from a QName in RDF Model?

From: Tim Bray <tbray@textuality.com>
Date: Thu, 09 May 2002 19:03:05 -0700
Message-ID: <3CDB2A59.7000108@textuality.com>
Cc: www-tag@w3.org
> Raised by: Jonathan Borden
>   http://lists.w3.org/Archives/Public/www-tag/2002Jan/0178
> 
> Raised date: 22 Jan 2002
> 
> Accepted by TAG 28 Jan 2002:
>   http://www.w3.org/2002/01/28-tag-irc

I have an action item to get some www-tag discourse going on this one.

Per the Namespaces REC, a qname can be seen as a two-tuple: namespace 
name, local name.  The namespace name is a URI reference.

In RDF, there is an explicit mechanism for turning these into URIs: 
concatenate the namespace name and the local name.  For this reason, 
namespaces for RDF applications often end in '#' or '/'.

Qnames work effectively as universally-unique labels in markup 
applications.  Given that the Web has as one of its bases the notion of 
the universal flat URI namespace, it would seem desirable to express a 
qname as a URI, as is done in RDF.  That is to say, given any element 
type (in the XML 1.0 sense) that was a qname, it would have its own URI 
that you could use to talk about it and potentially retrieve information 
about it.

It wouldn't be that hard to write a simple rule for mapping qnames to 
URIs.  A little thought shows that it the mapping would have to be 
reversible, which adds to the difficulty, but is certainly not 
insuperable.  It might not be possible to be entirely compatible with 
the way RDF 1.0 has done this, but perhaps it's not too late to fix RDF.

So the first-level questions to address are:

- is this a good thing to do?
- how important is it, relative to all the other things the W3C needs to 
worry about?

There's a meta-question that goes along with these.  If every qname 
becomes a URI, the question arises of what the URI addresses.  These 
would be useful, just as namespaces are useful, even in the absence of a 
resource representation to be obtained by dereferencing.  On the other 
hand history shows that people expect URIs to be dereferencable and are 
confused when they're not.  RDDL (http://www.rddl.org) is an example 
that shows the kind of thing you might want to get by dereferencing this 
kind of namespace URI).  Assuming that it's a good idea to map qnames to 
URIs, is it necessary at the same time to solve the issue of what they 
should point at (which BTW is TAG issue #8).  -Tim
Received on Thursday, 9 May 2002 22:03:15 GMT

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