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

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.

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?


Received on Monday, 6 March 2006 21:53:44 UTC