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Re: [namespaceDocument-8] RDF and RDDL

From: Tim Berners-Lee <timbl@w3.org>
Date: Fri, 12 Apr 2002 08:44:53 -0400
Message-ID: <03ea01c1e21f$d8463d70$ac01a8c0@CREST>
To: <www-tag@w3.org>, "Tim Bray" <tbray@textuality.com>

From: "Tim Bray" <tbray@textuality.com>
> At 01:43 PM 08/04/02 +0100, Williams, Stuart wrote:
> 
> >We are now left with the question of whether http://www.rddl.org/#Nature
> >names a type of XML element or whether it identifies a fragment within a
> >RDDL document.
> 
> The interpretation of '#Nature' is different depending on whether 
> it's pointing into an XHTML file (whether it's a RDDL or not) or
> an RDF schema or whatever.  I don't think there's room for
> confusion.

But alas, there is at the moment.  When we advocate using RDF in XHTML
we don't have that distinction any more between the two types of document.

So we either have to:

1) -specify the architecture for XML so that the thing referred to
by a #idvalue reference to an XML document depends on not the
MIME type simply, but for a mixed namespace document itself, the
namespace of the identified element; or

2) - change XHTML and its MIME type to know about embedded
 RDF and specify its meaning; or

3) specify the architecture so that the semantic web langauges
  always use #idvalue to refer to the abstract thing described by
  a bit of XML, while  hypertext languages always mean the
  bit of the document; or

4) Just don't mix HTML and RDF, as it will always be confusing to
  have two parts of the meaning of a document.

My gut feeling is to go for 3.  I think 1 means that you can't
use fragids to point to a generic bit of XML when
just doing XML text processing.  Solution 2 doesn't solve
the general problem, and will need n^2 fixes for n langauges.
Solution 3 has the problem that the same URIref s being
associated with two different levels of meaning in different
contexts, which on the face of it violates the rule that the same
URI always refers to the same thing, but actually doesn't
as you just say that they both refer to the bit of document
but there is an implicit dereference operation in every use
of a URIref in a semantic web langauge.  This is, I think, normal,
as for example a graphic language which refers  to a circle
by URIref does refer to the circle not the bit of XML. 
 
> >This is of course just a variant of whether http://www.rddl.org/ names a
> >namespace or a namespace document.

((This particular one is not a problem so long as the namespace docuemnt
and the namespace are in 1:1 correspondence.  It is a bit like asking
whether "Stuart" idenifies you or your name.  In different contexts, there
is a different level of consistent, implicit, dereferencing.  I ask
you, what is your name?  and you say, "Stuart".  I ask you, who are
you?, and you say, "Stuart". If you were doing it in semantic web labguage
you would be more careful and say that you are [ contact:giveName "Stuart"]
but normally on forms there is an understanding that when asked for
"next of kin" you are asked for the name of your next of kin.))
  
Tim BL
Received on Friday, 12 April 2002 08:44:47 GMT

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