Re: Interpretation of RDF reification

On Thursday 23 March 2006 16:44, Peter F. Patel-Schneider wrote:
> From: Chris Dollin <kers@hplb.hpl.hp.com>
> Subject: Re: Interpretation of RDF reification
> Date: Thu, 23 Mar 2006 16:24:18 +0000
>
> > On Thursday 23 March 2006 15:44, Peter F. Patel-Schneider wrote:
> > > Not really.  OWL in RDF gives you much more than specialized relations.
> > > Much of the power of OWL comes from syntax that is more than just
> > > single relations.  It so happens that it is possible to embed OWL in
> > > RDF in a certain manner.  (This is not always possible, by the way, and
> > > OWL is very close to the maximum expressiveness that can be so embedded
> > > in RDF.)
> >
> > Could you articulate which bits of OWL semantics are /more/ than the
> > semantics given by the meanings of the OWL predicates and classes?
>
> From
> OWL Web Ontology Language
> Semantics and Abstract Syntax
> W3C Recommendation 10 February 2004
> Section 5

(snipped)

That's not ... quite what I meant by an articulation, but I'll brood on it,
since the core seems to be:

> You will notice that these semantic conditions are not on particular
> OWL predicates and classes but are instead on combinations of triples.

And:

> > > > So if you take the relation owl:inverseOf then this is just an [RDF]
> > > > relation.
> > >
> > > Well, sure, owl:inverseOf is *just* an RDF property, in RDF.  In OWL,
> > > on the other hand, owl:inverseOf is a special property - it has a extra
> > > meaning provided by the OWL semantics.
> > >
> > > > But it is linked to the following well known rule:
> > > >
> > > > { ?r1 owl:inverseOf ?r2 .
> > > >    ?a ?r1 ?b .  } => { ?b ?r2 ?a . } .
> > >
> > > Not all all.  There are *no* rules in RDF, nor in OWL.  The above is
> > > not even legal RDF syntax, nor legal OWL syntax.
> >
> > The OWL defining document isn't written on OWL, but that doesn't stop
> > it defining the OWL semantics.
>
> Sure, but so what?

So documents that aren't written in RDF or OWL can define the semantics 
of RDF or OWL, eg the meaning of `inverseOf`; so your objection to the
rule-snippet quoted above 

    >>> The above is not even legal RDF syntax, nor legal OWL syntax.

to the rule-snippet quoted above doesn't seem to hold.

> > When I introduce an predicate into my RDF -- say, kers:birthDate -- I
> > can explain what that predicate /means/ to people who want to use it.
> > I can't state that meaning in RDF, I can't state it in OWL, I can't teach
> > the machine what it means - but it's useful because it has that meaning,
> > and I can say that the statement `kers:Chris kers:birthDate 1-Jan-2006`
> > is false. The /RDF/ semantics doesn't do that, but it doesn't stop me
> > doing it.
>
> Yes, the RDF semantics doesn't do that, and the RDF semantics is all there
> is to RDF itself.  You are adding your own intended meaning to the things
> you write.  There is nothing wrong with this, in fact, it is pretty much
> required to proceed at all.  However, you do need to know that your
> intended meaning is not part of RDF, and that others who read your RDF are
> not obligated to put your intended meaning on it.

Of course. And neither am I obliged to put the intended OWL meaning on
an OWL predicate. Whether or not I do is a pragmatic matter, just as is
whether or not someone(s) accept and use my definition for kers:birthDate.

Isn't it?

-- 
Chris "x.f(y) == f(x, y) == (x, y).f" Dollin
The shortcuts are all full of people using them.

Received on Friday, 24 March 2006 13:31:00 UTC