- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Mon, 06 Mar 2006 18:26:32 -0500 (EST)
- To: franconi@inf.unibz.it
- Cc: eric@w3.org, connolly@w3.org, public-rdf-dawg-comments@w3.org
From: Enrico Franconi <franconi@inf.unibz.it> Subject: Re: [OK] Re: [OK?] Re: comments on "SPARQL Query Language for RDF" (Non-respect for RDF Semantics) Date: Mon, 6 Mar 2006 22:53:28 +0100 > On 3 Mar 2006, at 14:02, Peter F. Patel-Schneider wrote: > > For the record, the issue shows up when querying an RDF store that > > has been > > given > > ex:a ex:p ex:c . > > ex:a ex:p _:c . > > The behaviour of SPARQL depends on the behaviour of the RDF store. > > The RDF > > store might end up leaning its input, and thus only store > > ex:a ex:p ex:c . > > or it might maintain the input "as is". My view is that both > > stores are > > "correct", and that querying should not be able to distinguish > > between the two > > behaviours. > > > > However, the SPARQL basic query > > ex:a ex:p ?c . > > would (most likely) have one match in the leaning case, but two > > matches in > > the non-leaning case. > > Peter, > you are right with this example. > However, please note that the problem of answering in this richer way > is np-hard - since you can easily encode the problem of computing > lean graphs into this reacher query answering problem. And I guess it > is fine not to impose hard computational constraints in this phase. > > > (This also depends on just how the scoping graph is determined.) > > Mmhh, I'd say that it does not depend on that: the answer is uniquely > determined up to bnode renaming. Why are you saying that? Well, changing the scoping graph can change the permissable answers, or at least that is what I believe based on the SPARL documents. > cheers > --e. peter
Received on Monday, 6 March 2006 23:26:46 UTC