- From: Enrico Franconi <franconi@inf.unibz.it>
- Date: Wed, 18 Jan 2006 11:55:58 +0100
- To: Pat Hayes <phayes@ihmc.us>
- Cc: Dan Connolly <connolly@w3.org>, Bijan Parsia <bparsia@isr.umd.edu>, RDF Data Access Working Group <public-rdf-dawg@w3.org>
On 18 Jan 2006, at 04:58, Pat Hayes wrote: >> But, you probably did not pay attention to our text: >> "In fact, with the proviso that bnodes are not allowed to appear >> in pattern solutions, SPARQL may be extended to provide a way to >> override the default "simple entailment" with "RDF entailment", >> "RDFS entailment" (as defined in [RDF-MT]), and "OWL >> entailment" (as defined in [OWL-Semantics], where the syntactic >> restrictions in OWL-DL or OWL-Lite should be reflected in suitable >> syntactic restrictions on the form of basic graph patterns)." >> >> So, we suggest an upward compatible extension *without* bnodes in >> the answer, because it is the only one which we know is going to >> work for sure (it is easy to see this). As our latest interactions >> proved, it is an open research problem how to have a query >> language with bnodes in the answer based on entailment which can >> also smoothly work with simple entailment. > > I am still bothered by the possibilities of OWL-specific notions of > redundancy in answer sets. Consider an OWL/RDF KB that asserts > > :a rdf:type :A > :a rdf:type :B > :a rdf:type :C > :A rdf:type owl:Class > :B rdf:type owl:Class > :C rdf:type owl:Class > > and an OWL query > > SELECT ?x WHERE {:a rdf:type ?x .} Look, this is not a legal OWL-DL query. We pointed out in our old proposed text (and also in the new one). We allow in OWL-DL only queries that carry similar syntactic restrictions as OWL-DL expressions. This boils down to allow only for non-high order RDF graphs as BGPs (defined in [1]). So the above query is not of our concern in OWL-DL. As far as OWL-full is concerned, my very personal position is that I don't care, since I don't believe it makes *currently* any sense at all :-) So, whatever you say about OWL-full, is fine for me... > Now, this dataset OWL-entails the *existence* of a triple > intersection and three double intersections, all with :a in them. > So are these reasonable answer bindings for such a query? I see no > good reason why they should not be: in fact, one could reasonably > take the position that the *only* non-redundant answer here would > be to bind ?x to a term representing the most restrictive > intersection. But to construct such a term would require the use of > the RDF collection vocabulary when presenting the answer. Even if we allow high-order queries like the above in OWL-DL, the scoping set B would be restricted to be URIs in OWL-DL, so the problem doesn't show up in OWL-DL anyway! And, again, as far as OWL-full is concerned, see above :-) > I'd be interested in your reaction to the suggestion for how to > define 'extensions'. I tried to keep the basic structure of the > definition, but remove just the parts that might need to be > reconsidered more carefully. But in the light of the above, perhaps > I was trying to be too ambitious. I really like your idea of the scoping set B. See my other email. cheers --e. [1] Jos de Bruijn, Enrico Franconi, Sergio Tessaris (2005). Logical Reconstruction of normative RDF. Proc. of the Workshosp on OWL Experiences and Directions (OWLED 2005), Galway, Ireland, November 2005. <http://www.inf.unibz.it/~franconi/papers/owled-05.pdf>
Received on Wednesday, 18 January 2006 11:03:26 UTC