- From: Michael Kifer <kifer@cs.sunysb.edu>
- Date: Mon, 12 Dec 2005 20:20:46 -0500
- To: Bijan Parsia <bparsia@isr.umd.edu>
- Cc: "Evan K. Wallace" <ewallace@cme.nist.gov>, public-rif-wg@w3.org
> 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
Received on Tuesday, 13 December 2005 01:20:53 UTC