- From: Dan Connolly <connolly@w3.org>
- Date: 16 Oct 2002 11:18:47 -0500
- To: Jos De_Roo <jos.deroo.jd@belgium.agfa.com>
- Cc: Ian Horrocks <horrocks@cs.man.ac.uk>, Pat Hayes <phayes@ai.uwf.edu>, www-webont-wg@w3.org
On Tue, 2002-10-15 at 16:47, Jos De_Roo 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... > > I'm not agnostic at all... > i.e. I can't see how to write > (forall x,y P(x,y) -> A(y)) -> Range(P,A) > in Horn-clauses or in Datalog > (although I like nested implications > in propositional proof arguments) Oohh; that's quite compelling... currently, you can implement a complete RDFS reasoner with a horn/datalog reasoner. If we changed range to IFF, it's not clear that this property would hold. Likewise for subClassOf. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Wednesday, 16 October 2002 12:18:18 UTC