From: Dan Connolly <connolly@w3.org>

Date: 15 Oct 2002 13:31:12 -0500

To: Pat Hayes <phayes@ai.uwf.edu>

Cc: Ian Horrocks <horrocks@cs.man.ac.uk>, www-webont-wg@w3.org

Message-Id: <1034706673.26925.196.camel@dirk>

Date: 15 Oct 2002 13:31:12 -0500

To: Pat Hayes <phayes@ai.uwf.edu>

Cc: Ian Horrocks <horrocks@cs.man.ac.uk>, www-webont-wg@w3.org

Message-Id: <1034706673.26925.196.camel@dirk>

On Fri, 2002-10-11 at 18:07, pat hayes wrote: > > > > > >> Range(P, A) -> (forall x,y P(x,y) -> A(y) ) > >> > >> You want > >> > >> Range(P,A) <-> (forall x,y P(x,y) -> A(y) ) > >> > >> They are about equally clear and intuitive; but the latter rules out > >> some possibilities which the former permits. I believe that all the > >> 'intuitive' entailments that people want in fact hold in both these > >> cases; and that the former is therefore to be preferred. > > > >I am agnostic about which of these is to be preferred - as a humble > >engineer, all I need to know is which one it is so that I have a clear > >spec to which I can build my systems. I'm kinda agnostic too... I was leaning toward the IF, rather than the IFF... But, for what it's worth, I happened to bring it up in conversation with TimBL, and he expects the IFF meaning. "Anybody who says P rdfs:range rdfs:Resource is wasting their breath"; i.e. that's axiomatically true, to his mind. > >One point that is worth making though is that there are a number of > >similar statements that can be made about OWL properties, and that it > >may make sense to give them a uniform semantics, i.e., all treated as > >implication or all treated as bi-implication. E.g., we also have: > > > >Domain(P,C) implies/iff (forall x,y P(x,y) -> C(x)) > >TransitiveProperty(P) implies/iff (forall x,y,z (P(x,y) ^ P(y,z)) -> P(x,z)) > >SymmetricProperty(P) implies/iff (forall x,y P(x,y) -> P(y,x)) > >FunctionalProperty(P) implies/iff (forall x,y,z (P(x,y) ^ P(x,z)) -> y=z) > >InverseFunctionalProperty(P) implies/iff (forall x,y,z (P(y,x) ^ > >P(z,x)) -> y=z) > >inverseOf(P,Q) implies/iff (forall x,y P(x,y) -> Q(y,x)) > > How about all the unary properties of properties having an IFF > semantics? OK by me. > That would make sense, but it would leave domain, range > and inverse up for discussion. I prefer IFF for those too. But not too strongly. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/Received on Tuesday, 15 October 2002 14:30:37 GMT

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