Re: Possible semantic bugs concerning domain and range

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/