Re: [namespaceDocument-8] RDF and RDDL

Tim Berners-Lee wrote:
> From: "Tim Bray" <>
> > At 01:43 PM 08/04/02 +0100, Williams, Stuart wrote:
> >
> > >We are now left with the question of whether
> > >names a type of XML element or whether it identifies a fragment within
> > >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.

Right. RDDL using XLink doesn't have this problem, as _the transform_
converts into RDF which defines the meaning (e.g. In my mind this transform is a
mathematical equation which defines the meaning of the RDDL/XLink document
_as_ RDF i.e. it is unambiguous.

So we either have to:
> 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

yes, exactly. (this is how I've viewed RDDL all along).

> 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.

Just as a frag id pointing to the XML representation of an RDF Schema or OWL
ontology, points to the piece of XML where the Class is defined. This seems
quite normal to me.

> > >This is of course just a variant of whether names
> > >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've been considering the XML Schema as namespace document issue in much
more depth recently, as part of WebOnt, which needs to integrate the XML
Schema and WebOnt type hierarchies ... note that RDFS does this as well e.g.
RDF Datatypes.

I am reasonably certain that is possible to develop a canonical transform
that represents an XML Schema _as_ RDF, particularly in the Ontology Web
Language. If this is actually possible, and some recent work does indeed
suggest this is possible, then my objection to having a namespace point
directly to an XML Schema is much much less.


Received on Friday, 12 April 2002 09:51:15 UTC