- From: Bijan Parsia <bparsia@isr.umd.edu>
- Date: Wed, 22 Jun 2005 14:03:52 -0400
- To: Jos de Bruijn <jos.debruijn@deri.org>
- Cc: public-sws-ig@w3.org, Jim Hendler <hendler@cs.umd.edu>, dreer@fh-furtwangen.de
On Jun 22, 2005, at 1:18 PM, Jos de Bruijn wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Jim Hendler wrote: > >> Jos- >> that's not quite right as I understand it - to use an example from the > paper I cited - >> >> Given an ontology containing only a single RDF triple: >> <#pat> <#knows> <#jo>. >> the answer to a query asking if pat knows exactly one person would be > "no" under >> RDF's open world semantics, but "yes" under the closed world semantics > of Datalog. >> >> there's no negation explicit here. > > If you would write down the query you mentioned, you would see that > the query includes negation. [snip] That's the point, right? Queries that you might expect to return the same results on that data *don't* depending on the semantics you have for the *data*. Of course your query language might be (will be!) more expressive than your data language (see SQL). So the question is how to make this work. Are we already in the land of multiple extensions (in the default theory sense)? One hopes not. One reason to be less shy of, e.g., NAF in query languages rather than in the data is that the author of the query is most likely the person evaluating the query, so its context is rather clearer. Cheers, Bijan.
Received on Wednesday, 22 June 2005 18:03:55 UTC