On 13 Dec 2005, at 01:57, Bijan Parsia wrote: > 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. > But, be that as it may, clearly the text in the minutes is a boo > boo (and definitely not the scribes fault). To add even more noise to this discussion, I can say that even though the algebra on top of basic SPARQL still needs some semantic clarification, there is some evidence that the OPTIONAL construct introduces some limited form of difference. --e.Received on Tuesday, 13 December 2005 01:26:30 GMT
This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 2 June 2009 18:33:25 GMT