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Re: On told-bnodes in queries

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 2 Nov 2005 21:45:03 -0600
Message-Id: <p06230911bf8f36b1db7d@[192.168.2.2]>
To: Enrico Franconi <franconi@inf.unibz.it>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>On the other hand, I don't believe that your alternative semantics 
>based on "union" works.
>Here is the counterexample - the same as before :-)
>
>GRAPH: :s :p _:b .
>
>query:  { ?x :p _:a }
>
>where we mean _:a in the query to be used as a told bnode.
>Well, I expect to get the empty set as the answer, but with your 
>union semantics I get [?x/:s].

But this case is impossible. The only way such a bnode can occur in a 
query is if it were provided as a binding to a variable in a previous 
query on the same graph. So the bnode must occur in the graph 
somewhere. Then creating the union will cause the bnode in the 
(subsequent) query to be identified with its previous occurrence in 
the graph.

Pat


>cheers
>--e.


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Received on Thursday, 3 November 2005 03:45:12 GMT

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