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Re: Current agreement upon named graphs

From: David Booth <david@dbooth.org>
Date: Fri, 09 Nov 2012 09:15:30 -0500
To: Olivier Rossel <olivier.rossel@gmail.com>
Cc: semantic-web@w3.org
Message-ID: <1352470530.2269.7018.camel@dbooth-laptop>
On Fri, 2012-11-09 at 13:38 +0100, Olivier Rossel wrote:
> I have been out of the semantic web for some time, and I would like to know
> the current agreement upon named graphs.
> 
> Here are my questions:
>  - can a triple belong to several named graphs?

Yes.

>  - can the argument of the SPARQL "GRAPH" keyword  be *a list* of named graph?
> if yes, is this list considered to be the union of all those named graphs?

No, not directly as the argument of the GRAPH keyword -- the syntax is a
bit different.  But a SPARQL query can specify multiple graph sources
such that the union of those graphs is queried.  See:
http://www.w3.org/TR/sparql11-query/#namedGraphs 

>  - is there a plan to investigate algebra of named graphs, such as :
> (namedGraph1 && !namedGraph2) || namedGraph3?

Not in SPARQL as you've written it, but you can write SPARQL queries
that give the effect of an algebra of results using keywords such as
UNION, EXISTS and NOT EXISTS.  (Intersection is computed by default and
does not use a keyword.)  See:
http://www.w3.org/TR/sparql11-query/#alternatives
http://www.w3.org/TR/sparql11-query/#negation

David

> 
> Any comment is welcome.
> 
> Cheers,
> 
> Olivier.
> 
> 
> 

-- 
David Booth, Ph.D.
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
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Received on Friday, 9 November 2012 14:16:07 GMT

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