- From: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
- Date: Fri, 27 Aug 2010 20:03:34 +0100
- To: Axel Polleres <axel.polleres@deri.org>
- Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
On 27 August 2010 17:42, Axel Polleres <axel.polleres@deri.org> wrote: > Hi Birte, all, > > Do you think we should add a test case like that: > > G: > :s :p "foo" > > Q: > SELECT ?L > WHERE { ?L a rdfs:Literal } > > Similarly: > > G: > :s :p 1 > > Q: > SELECT ?L > WHERE { ?L a xsd:integer } > > > Obviously, those will not give an answer, but some people might expect those to return surrogate blank nodes... a colleague of mine just came to me with that (in a different context), and I thought I might share it. Blank nodes should not be returned according o the regime.They are treated like Skolem constants, i.e., you could rename them in the graph as you want before answering the query, but then you just return the ones that are actually in the graph and in this case there is none. Apart from that any binding will be invalid RDF anyway, but if you were to neglect that (or if we assume RDF is extended to allow for literals in subject position), then under RDFS reasoning, you could get "foo", but not "abc" or "whatever" since only "foo" occurs in the graph and we limit bindings to the vocabulary of the graph and the RDFS vocabulary (rdf:_1, rdf:_2, ... have special treatment) and literals are only in the vacabulary if they occur in the graph. If we include it as a test, we might get different answers because some systems are strict and don't allow literals whereas others are not that strict and I am not sure we want to punish that? If we were, one could ask why SPARQL not just says that any up-to-date RDF is allowed, but SPARQL explicitly allows literals in subject position. The conditions on ent. reg. require, however, that any instantiated BGP is legal for the regime and "foo" a rdfs:literal is not legal RDF(S). Birte > Axel -- Dr. Birte Glimm, Room 309 Computing Laboratory Parks Road Oxford OX1 3QD United Kingdom +44 (0)1865 283520
Received on Friday, 27 August 2010 19:04:07 UTC