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Re: model theory for RDF/S

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Thu, 27 Sep 2001 13:05:24 -0400
To: connolly@w3.org
Cc: phayes@ai.uwf.edu, www-rdf-logic@w3.org
Message-Id: <20010927130524E.pfps@research.bell-labs.com>
From: Dan Connolly <connolly@w3.org>
Subject: Re: model theory for RDF/S
Date: Thu, 27 Sep 2001 10:40:57 -0500

> "Peter F. Patel-Schneider" wrote:
> [...]
> > Syntax:
> > 
> > URI is the collection of URI names, i.e., some collection of strings
> > 
> >   [NB:  This ignores all aspects of the structure of URIs.]
> > 
> > L is the collection of literals, i.e., some collection of strings,
> > disjoint from URI
> 
> I think the mention of "string" here is a misnomer/red-herring, no?
> 
> i.e. take the string "http://example/". It's a URI, and
> you say URIs are disjoint from literals... hence it's not a literal.
> 
> But it's a perfectly legal property value in RDF:
> 
> 	<rdf:Description rdf:about="#something">
> 	  <dc:identifier>http://example/</dc:identifier>
> 	</rdf:Description>
> 
> I think if you just say URI and L are disjoint, denumerable
> sets, you've said what you need to say.

Yes, that should mostly work, at least for the purposes of this
discusssion.  I don't know if you even need to say denumerable.


> > 3. if <f,g> is in E
> >    then I(E) = true
> 
> you mean I(<f,g>) rather than I(E), no?

Correct.  I have this typo in several other places also.

> > Claim 1:
> > 
> > A core RDF interpretation that is a model of a basic untidy RDF graph R
> > contains everything (and more) that is in the intended core RDF (i.e., RDF
> > without reification or containers) meaning of R.  In other words, a model
> > contains all the information implicitly (or explicity) in the graph, and
> > maybe more, and contradicts nothing that is implicitly (or explicitly) in
> > the graph.
> 
> Hmm... at this point, the formality fails me. I would need
> an example to provide intiutions about whether I believe this
> or not.

Think of this as a very informal way of stating that we need only consider
the models of a graph, not the graph itself, to get all the results we
want, whatever they are.  For example, we would say that one graph implies
another precisely when all the models of the second graph are also models
of the first.  We would also say that the results of a query operation can be
determined by looking only at the models of a graph.

> > Claim 2:
> > 
> > A core RDF interpretation that is not a model of a basic untidy RDF graph R
> > has something that is not compatible the intended core RDF meaning of R.
> > In other words, a non-model is missing or incorrect on something that is
> > implicitly (or explicitly) in the graph.
> 
> That makes sense relative to claim 1 (though I don't have
> a good feel for claim 1 itself).
> 
> > Claim 3:
> > 
> > For every basic untidy RDF graph R there is a core RDF interpretation that
> > captures exactly the closure of the intended core RDF meaning of R and that
> > is a model for R.  That is, roughly, that there is a model that makes
> > everything implicitly (or explicitly) in the graph true, and everything
> > else false.
> 
> I have no idea what the significance of this claim is, let
> alone any sense of whether I agree or disagree with it.

This claim roughly says that there is a ``canonical'' model.  That is you
don't need to worry about the fact that there are multiple models for a
graph, you can just work with this canonical model.

peter
Received on Thursday, 27 September 2001 13:05:35 UTC

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