Re: [all] OWL and RDF compatibility scribles

> On Dec 12, 2005, at 7:29 PM, Michael Kifer wrote:
> [snip]
> > There was a discussion of whether the query language (SPARQL) has 
> > negation
> > and Bijan said that the existentials get us there.
> > This is something that I don't understand. *Universal quantification* 
> > in a
> > query language introduces negation. But existential conjunctive queries
> > without explicit negation are Horn clauses and are within Datalog.
> > For those queries the classical equivalence of logical implication, 
> > least
> > fixpoint, and the unique min model holds.
> >
> > Bijan, please elaborate.
> 
> I'm trying to reconstruct what I was thinking...
> 
> Hmm.
> 
> I think it was a brain fart. That or I was conflating the difficulties 
> you get with RDF and OWL kbs.
> 
> Hmm.
> 
> I think I was thinking of counting, not negation, and how generated 
> individuals muck with that. But it came out seriously garbled.

If you meant counting or other aggregate then yes -- CWA and OWA might
give you different answers for things like count(...)=something. You can also
express negation with count(...)=0.

But does SPARQL allow this? I saw some discussion, but don't know how it
was resolved.


	--michael