- From: Axel Polleres <axel.polleres@deri.org>
- Date: Tue, 22 Sep 2009 12:02:35 +0100
- To: "Birte Glimm" <birte.glimm@comlab.ox.ac.uk>
- Cc: "SPARQL Working Group" <public-rdf-dawg@w3.org>
On 22 Sep 2009, at 11:44, Birte Glimm wrote: > Hi all, > I just wanted to confirm that I understand the specs correctly... > As I read the SPARQL query grammar, I understand it that literals are > allowed in subject position. Thus, a query such as > SELECT ?x WHERE { ?x rdf:type rdf:XMLLiteral } > under say RDF or RDFS entailment would have to return all valid RDF > XML literals (if not sufficently restricted) of which there are > infinitely many. Although RDF itself does not allow literals in > subject position, SPARQL queries do allow it and in fact according to > the RDF(S) semantics (under RDF(S) entailment) the statement XXX > rdf:type rdf:XMLLiteral is entailed by any graph for XXX a valid XML > Literal lexical form. All correct? > Birte > Hi Birte, interesting catch! However, I think that we have to look at it from the perspective of how extending BGP matching rather than purely from the definitions of RDF(S) entailment only: Section 12.6 of the current spec says here (there are people in the group who can probably shed more light on the meaning, in case I got it wrong): "For any basic graph pattern BGP and pattern solution mapping P, P (BGP) is well-formed for E." So, in your case: say you we have solution mapping binging ?X to literal "xyz", then P(BPG) = "xyz" rdf:type rdf:XMLLiteral . which is not an RDF Graph and thus not well-formed wrt. any entailment regime that falls under the scope of the BGP Matching extension, since the definition of well- formedness requires well-formedness and "An entailment regime specifies a subset of *RDF graphs* called well- formed for the regime" In other words, BGP matching extensions can only allow solutions which yield valid RDF Graphs when applied to the BGP. Agreed? cheers, Axel > -- > Dr. Birte Glimm, Room 306 > Computing Laboratory > Parks Road > Oxford > OX1 3QD > United Kingdom > +44 (0)1865 283529 > > -- Dr. Axel Polleres Digital Enterprise Research Institute, National University of Ireland, Galway email: axel.polleres@deri.org url: http://www.polleres.net/
Received on Tuesday, 22 September 2009 11:03:16 UTC