W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > March 2003

Re: (pfps-15) Re: Minutes of RDFCore WG Telecon 2003-02-24

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 11 Mar 2003 14:18:51 -0600
Message-Id: <p05111b27ba93c9c1f791@[]>
To: Graham Klyne <GK@NineByNine.org>
Cc: w3c-rdfcore-wg@w3.org

>At 08:25 11/03/2003 -0500, Eric Miller wrote:
>>ACTION: Gk to follow up on the concepts implication on pfps-15
>>(context: http://www.w3.org/2003/02/28-rdfcore-irc#T16-11-37)
>Can RDF say anything about anything?
>The RDF documents are contradictory on this point.  The Primer indicates
>that RDF can be used to let anyone ``say anything they want about existing
>resources'' with no exception for the resources used by RDF.  Concepts says
>that ``RDF is an open-world framework that allows anyone to make simple
>assertions about anything''.  However, Concepts also says that ``Certain
>URIs are reserved for use by RDF, and may not be used for any purpose not
>sanctioned the RDF specifications.''
>-- http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0148.html
>Is the comment I believe led to pfps-15.
>My follow-up here is this:  I think any Concepts implications of 
>pfps-15 will be picked up in dealing with pfps-16:
>RDF Concepts states
>         The expressive power of RDF corresponds to the
>         existential-conjunctive (EC) subset of first order logic [Sowa].
>How can
>         takes(John,book,school)
>be represented in RDF?
>How can
>         loves(John,spouse(John))
>be represented in RDF?
>How can the RDF and RDFS semantic conditions be represented in the
>existential-conjunctive subset of first order logic?
>-- http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0154.html
>Essentially, this (and maybe other) actions on Concepts require that 
>descriptions about the expressive power of RDF be tightened up.

Right, and this might be an opportunity for the other docs to mention 
the idea of semantic extension. This notion is pretty central to any 
discussion of what RDF 'means' but currently looks like an arcane 
abstract matter inside the MT.

The expressive power of a notation depends on its semantics.  We 
rather play fast-and-loose with this because we introduce new 
semantics when we add some vocabularies.  'Basic' RDF strictly has a 
very limited expressive power, but RDFS has quite a lot more and 
OWL-in-RDF has a lot more still. If these were all just RDF 
ontologies, ie if this were all *really* represented in pure RDF, 
this would be impossible, so we really need to explain what it means. 
Since each of these vocabularies comes with its own extra semantics, 
it strictly speaking has to be considered a separate language. But as 
far as parsers are concerned they are all RDF, of course. I chose the 
term 'semantic extension' partly to emphasize that they are not 
syntactic extensions.


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Received on Tuesday, 11 March 2003 15:18:52 UTC

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