- From: Richard Newman <rnewman@franz.com>
- Date: Sat, 5 Jul 2008 11:15:07 -0700
- To: Nuutti Kotivuori <naked@iki.fi>
- Cc: public-sparql-dev@w3.org, public-rdf-dawg@w3.org
Hi Nuutti, The short answer is "it depends". Longer is "it depends on the entailment regime chosen by the implementation": http://www.w3.org/TR/rdf-sparql-query/#sparqlBGPExtend Different entailment regimes can "expand" the graph against which a basic graph pattern matches. * Under simple entailment, only ns:a is returned. Typed and untyped literals are entirely different, and literals without language tags do not match those with tags. * Under a D-entailment regime which includes xsd:string and untyped literal equivalence, ns:a and ns:b would be returned. * Under an entailment regime which not only entails that equivalence, but also can deduce that dt:datatype is a subtype of xsd:string, ns:a, ns:b, and ns:c would be returned. It's also possible to conceive of an entailment regime which does something with language tags, but that would be less useful. Now, an implementation-specific aside: In AllegroGraph, we implement simple entailment, so you should get only the first result for a normal query. We also allow the user to apply wrappers to a triple-store -- e.g., an RDFS++ reasoner -- and this has the effect of making your SPARQL queries run against a different entailment regime (e.g., RDFS entailment with additions). It would be quite straightforward to write a new wrapper class that implemented xsd:string D-entailment. HTH, -R On 5 Jul 2008, at 7:42 AM, Nuutti Kotivuori wrote: > > Hello, > > I am having some trouble matching literals with SPARQL. It seems that > just about every implementation I tried manages to give me a differing > set of answers for a very simple query. I have tried to verify this > against the specification, but I haven't been able to find a > conclusive answer there. > > I believe this could be an important interoperability blocker for > several applications as the problem is easily triggered by the > simplest of graph patterns. > > The issue is very simple do describe, but to be exact so it can be > discussed reasonably, I will write it here somewhat verbosely: > > Assume the following RDF graph: > > *** > @prefix dt: <http://example.org/datatype#> . > @prefix ns: <http://example.org/ns#> . > @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . > > ns:a ns:p "value" . > ns:b ns:p "value"^^xsd:string . > ns:c ns:p "value"^^dt:datatype . > ns:d ns:p "value"@en . > *** > > Now, if this graph is queried with the simple SPARQL query: > > SELECT ?x where { ?x ns:p "value" } > > What should the result set be?
Received on Saturday, 5 July 2008 18:16:04 UTC