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Re: Inferencing on graph patterns

From: Ivan Herman <ivan@w3.org>
Date: Sat, 14 Nov 2009 06:30:40 +0100
Message-ID: <4AFE4080.3080708@w3.org>
To: Simon Reinhardt <simon.reinhardt@koeln.de>
CC: public-rdf-dawg-comments@w3.org
Dear Simon,

Thanks for your comments. And apologies for the somewhat late reply.

You wrote:
 > In trying to understand SPARQL 1.1 Entailment Regimes [1] I was
 > wondering if inferencing will ever take place on the RDF data in graph
 > patterns themselves. Consider the following data in a store:
 >
 > (1) ex:C1 rdfs:subClassOf ex:C2 .
 > (2) :myC1 a ex:C1 .
 >
 > Now when you do the following query at the endpoint for the store:
 >
 > SELECT ?type WHERE { ?x a ex:C1 , ?type }
 >
 > and it supports the RDFS entailment regime the result would be ex:C1 and
 > ex:C2 because the store would infer :myC1 to be of type ex:C2, either
 > when the data got added or on-the-fly.
 >
 > But what if the store didn't contain triple (2) and so no data about any
 > instances of those two classes? Is there any way that it could make
 > inferences about the data in the WHERE clause and therefore infer that
 > ?x would be of type ex:C2 as well? I guess not since this is querying by
 > matching patterns rather than "query by example". But I can see various
 > uses for this. So if this is not how it's currently defined to work,
 > have you considered this?

The inference regime is defined on possible solution. That indeed means
that no inference is made on variables which means, as you say, that
without  the triple (2) the required results will not be returned. And
there is  no mechanism envisioned in SPARQL to achieve that.

Note, however, that you may get what you want with a different query.
For  example, in this case, the

 SELECT ?type WHERE { ex:C1 rdfs:subclass ?type. }

will return all possible types.

Sincerely

Ivan
On behalf of the SPARQL Working Group


-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
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Received on Saturday, 14 November 2009 05:30:49 GMT

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