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Re: [OK] Re: [OK?] Re: comments on "SPARQL Query Language for RDF" (Non-respect for RDF Semantics)

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Mon, 06 Mar 2006 18:26:32 -0500 (EST)
Message-Id: <20060306.182632.35856633.pfps@research.bell-labs.com>
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 GMT

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