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Re: What is an RDF Query?

From: Sandro Hawke <sandro@w3.org>
Date: Mon, 17 Sep 2001 13:18:50 -0400
Message-Id: <200109171718.f8HHIoK31309@wadimousa.hawke.org>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
cc: www-rdf-rules@w3.org

> > Since I have trouble thinking in RDF graphs sometimes, I translate
> > them to a small subset of FOL for this kind of work.  Specifically, I
> > use the subset with only constants, existential variables, 2-ary
> > predicates, and conjunction.  (No universal variables, no negation, no
> > disjunction, no equality, and no logic functions.)
> 
> Again, this sort of thing is possible, and provides good insights into the
> meaning of RDF(S).  However RDFS is not captured by this subset of FOL, as
> RDFS requires that rdfs:subPropertyOf be transitive.  To make this
> intuition precise, you have to capture all of whatever you are considering,
> as even very small changes in the formalism have large consequence.

Before considering the entirely of your message, I'd like to check on
what you're saying here.  In saying "...RDFS is not captured by this
subset of FOL..." it sounds like you're presuming the KB should
capture the meaning of rdfs:subPropertyOf before we even get to our
"rules".  I'm presuming instead that our "rules" will capture the
meaning of rdfs:subPropertyOf.  That is, I'm assuming a basic system
will know nothing of rdfs (or reification or containers or even
rdf:types) until a set of rules providing the axiomatic semantics for
such things are loaded (in the same manner, whatever it may be, as
any other rules are loaded).

Does my approach here seem reasonable?  My big concern with it is that
I hear DAML+OIL cannot be expressed axiomatically in Horn logic.
Obviously there may be performance issues to this approach, but I
think that can be addressed behind the scenes, without changing the
general query/rule model.

   -- sandro
Received on Monday, 17 September 2001 13:22:45 GMT

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