W3C home > Mailing lists > Public > www-rdf-logic@w3.org > April 2001

Re: semantics status of RDF(S)

From: pat hayes <phayes@ai.uwf.edu>
Date: Fri, 6 Apr 2001 14:45:12 -0500
Message-Id: <v04210111b6f3cb89a336@[205.160.76.201]>
To: Aaron Swartz <aswartz@swartzfam.com>
Cc: www-rdf-logic@w3.org
>Peter F. Patel-Schneider <pfps@research.bell-labs.com> wrote:
>
> > All four of these triples have the same status as triples like
> >   { loves, john, mary }
> > and clutter up the semantic message of a document.
>
>Clutter up the semantic message? What is the problem here? You're saying
>something, and we're using triples to say it. The semantic message is clear.
>You are saying something about a statement, but not asserting the statement.
>The meaning of what you are saying is defined as all RDF properties are.
>
> > Yes, three of these triples use RDF reification predicates and so 
>can, maybe,
> > be ignored by RDF processors who are not interested in reified 
>statements (but
> > it is very dangerous to do so).  However, the first triple uses a predicate
> > that is in no way special to RDF and so I don't see how RDF processors and
> > applications can treat it in any other way than triples like
>
>No, they wouldn't treat it in any special way. They would merely interpret
>the semantics of your message properly. Since you are asserting a negation,
>you are not asserting the actual triple, so you are OK there.

Asserting a negation is more than simply not asserting the negated 
proposition: it is DENYING it. So if RDF supported negation, then an 
RDF processor should draw a conclusion from finding P and the 
negation of P: it ought to notice that they are contradictory. The 
central point, however, is that an RDF triple is supposed to assert 
that a relation holds; and negation is not a relation. So if it is 
encoded as an RDF relation, something needs to 'know' that this 
particular usage isnt meant to be taken literally in RDF, but is 
simply a usage of the RDF datamodel to encode something else. And 
indeed RDF, like any other system of linked arcs which allows one to 
build arbitrarily complex labelled graphs, can be used to encode (the 
syntax of) other languages in this way. But that isnt using RDF to 
express negation: it is using RDF datastructures to encode the syntax 
of some other language which expresses negation.

Pat Hayes

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Received on Friday, 6 April 2001 15:43:11 GMT

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