- From: Steve Harris <steve.harris@garlik.com>
- Date: Thu, 24 Sep 2009 10:31:36 +0100
- To: "public-rdf-dawg@w3.org Group" <public-rdf-dawg@w3.org>
On 24 Sep 2009, at 10:16, Bijan Parsia wrote: > On 24 Sep 2009, at 10:01, Steve Harris wrote: > [snip] >> My understanding is that it is a legal query, it's prohibited >> neither by the syntax, nor the query algebra. >> >> However, it can't ever match any RDF triples in the query >> processors data, as there can be no legal triples with literal >> subjects. > > Without inference. In the presence of RDFS interpretations, there > are situations where one might reasonably think that > "<foo/>"^^rdf:XMLLiteral rdf:type rdfs:Literal. > > is entailed by: > :s :p "<foo/>"^^rdf:XMLLiteral. > > The only thing preventing that entailment would be a syntactic > restriction on the form of things entailed (e.g., if we restrict > ourselves to legal RDF graphs.) SPARQL/Query 1.0 is restricted to legal RDF graphs though, as per (my reading at least) of section 12.6. >> I don't remember the exact motivation, though I seem to remember >> that it came up in discussion in the DAWG group, but it does give >> us a level of future proofing, and allows systems which allow >> literal subjects to easily extend SPARQL to query their full data. > > I guess the relevant question is do we want RDFS entailment in > SPARQL queries to work strictly on RDFS graphs, in which case: > ASK WHERE {"<foo/>"^^rdf:XMLLiteral rdf:type rdfs:Literal.} > is always false, or work with ground BGPs, in which case that query > would sometimes return true. (E.g., against the above triple). > > In other words, are we in the future we proofed against :) Heh, perhaps :) I think currently it's always false, due to 12.6. Certainly there are RDF-like systems which permit literals in the subject position, so for some people at least it is significant. - Steve -- Steve Harris Garlik Limited, 2 Sheen Road, Richmond, TW9 1AE, UK +44(0)20 8973 2465 http://www.garlik.com/ Registered in England and Wales 535 7233 VAT # 849 0517 11 Registered office: Thames House, Portsmouth Road, Esher, Surrey, KT10 9AD
Received on Thursday, 24 September 2009 09:38:58 UTC