Re: Interpretation of RDF reification

From: "McBride, Brian" <brian.mcbride@hp.com>
Subject: RE: Interpretation of RDF reification
Date: Thu, 23 Mar 2006 13:47:17 -0000

>  
> > 
> > I don't understand the difference.  RDF just does not have 
> > the expressive
> > power to do this sort of thing.   It just like asking whether 
> > propositional
> > logic could express something like "All students are people."
> 
> I think that answers my question.  
> 
> I'm confused about how semantics of [OWL] relate to the semantics of RDF.

Roughly in the way that propositional logic relates to predicate logic (at
least if you think of propositional logic in a certain way).  There are
"more" constructs in OWL, and these constructs have meaning that cannot be
expressed in RDF.  The only strangeness is that the extra OWL constructs
are actually written as (collections of) RDF triples, but nonetheless the
added expressive power is still real.

> In a similar vein, does RDF have the expressive power to define local
> domain and range constraints?  

Certainly not.

> Not in itself, but I think of [OWL] as an
> RDF vocabulary that extends RDF, and can express such constraints.  So
> in one sense RDF does have the expressive power to represent local
> domain and range constraints, but it needs the OWL vocabulary to do so.

No, no, a thousand times no!

Just using owl:sameAs in RDF does *NOT* get you any part of the OWL meaning
of owl:sameAs.  This is a complete falsehood that nonetheless seems to
occur over and over.  It needs to be vigorously eliminated whereever it
occurs.

> I'm interpretting your answer as saying that one couldn't have an RDF
> voculary the expressed the sort of structures I suggested around
> marriage and Marriage without extending the RDF syntax.

Well, not really.  After all, syntax is not the same as semantics.  This is
demonstrated by the relationship between RDF and OWL.

> At this point I should cease to tax your patience and go read a book on
> logic if I really want to understand the answer.

Hmm.   I was trying to think of what logic book would make this clear.
Perhaps Bijan Parsia would know.

> Brian

peter

Received on Thursday, 23 March 2006 14:58:39 UTC