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Re: need to determine what RDF is

From: Dan Connolly <connolly@w3.org>
Date: 30 May 2002 16:41:15 -0500
To: patrick hayes <phayes@ai.uwf.edu>
Cc: danbri@w3.org, bwm@hplb.hpl.hp.com, www-rdf-comments@w3.org, em@w3.org, w3c-semweb-cg@w3.org, pfps@research.bell-labs.com
Message-Id: <1022794876.25653.256.camel@dirk>

On Thu, 2002-05-30 at 11:10, patrick hayes wrote:
> >On Thu, 2002-05-30 at 10:26, Peter F. Patel-Schneider wrote:
> >[...]
> >>  I'm only interested in relationships between RDF graphs.  Which such
> >>  relationships are RDF relationships? 
> >>
> >>  My view is that the only such relationships are RDF entailment and RDFS
> >>  entailment.  Any agent that computes any other relationship between RDF
> >>  graphs is not doing RDF.
> >
> >Why is RDFS special? It's just the first of many RDF vocabularies,
> >no?
> Its more than just an RDF vocabulary because it has some extra 
> semantic conditions.

That doesn't look special, to me; I expect each vocabulary
to come with some extra semantic conditions.

> For example, if RDFS is considered purely as an 
> RDF vocabulary, then rdfs:subClassOf is not required to be 
> transitive;


How does 'RDF vocabulary' get that meaning?
Never mind; I'll stop using 'RDF vocabulary' if
that's what it means to you.

> in fact, there is no way to express transitivity of a 
> property in RDF.

Right; we wrote it in semi-formal english in the spec
(and in rdf:comment's, I think).

> Considered as RDFS, however, it is required to be 
> transitive. The distinction is made exact in the MT document by 
> distinguishing between RDF-entailment and RDFS-entailment. In 
> general, if a particular vocabulary has some extra semantic 
> conditions attached to it, then there will be a new notion of 
> entailment (I used the generic term 'vocabulary entailment' for this 
> idea in the MT document: 
> http://www.w3.org/TR/rdf-mt/#NameSpaceEntailment ).

Yes, of course; and then there are all the notions of entailment
we get by combining these vocab... er... extensions.

That's what I meant by "lots of formalisms in the framework"
over in rdf-logic.

> Most RDF 
> vocabularies, eg dublin core, RSS, have no extra semantics attached 
> to them.

Yes, I think they do.

The semantics may be informal -- we might not be able
to communicate them to a machine -- but there are certainly
interpretations that are *not* consistent with the
specification of dc:title; to wit, any interpretation
	<http://www.w3.org> dc:title "apples and oranges".

> DAML+OIL certainly does, of course, but then I wouldn't even 
> call that an RDF vocabulary in any ordinary sense (yet).
> RDFS is also special because its specified in the RDF specs, I guess.

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 30 May 2002 18:41:32 UTC

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