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Re: why I don't like default graphs in the DATASET proposal

From: Axel Polleres <axel.polleres@deri.org>
Date: Tue, 4 Oct 2011 07:05:32 +0200
Cc: SPARQL Comments <public-rdf-dawg-comments@w3.org>
Message-Id: <90102DA2-9136-4F04-9DA6-273D6C30BDED@deri.org>
To: Richard Cyganiak <richard@cyganiak.de>
Hi Richard,

(answering here only on the comment to the SPARQL-comments list and thus removed the RDF WG in cc:)

> >> An RDF Dataset comprises one graph, the default graph, which does not
> >> have a name, and zero or more named graphs, where each named graph is
> >> identified by an IRI.
> 
> You are right. If taken literally, this definition [1] implies that an RDF Dataset can't have the same triples in the default graph and in a named graph. This clearly isn't the intention, so the wording is a bug in the SPARQL spec and needs to be fixed.

I don't see how the wording at [1] would imply disjointness of the named and default graphs. 
Since a *named graph* is a *pair* of a graph and its name (as indeed made more explicit in [2]), 
any named graph is per definition different from the default graph or from any other named graph, so 
I don't think that the wording  at [1] is buggy.

best regards,
Axel


On 30 Sep 2011, at 11:28, Richard Cyganiak wrote:

> Hi pa,
> 
> (cc SPARQL comments list)
> 
> On 29 Sep 2011, at 16:57, Pierre-Antoine Champin wrote:
> > I realize that a statement that I made:
> >
> > On 09/29/2011 04:42 PM, Pierre-Antoine Champin wrote:
> >> I know that SPARQL does not require that the default graph is *also*
> >> present as a named graph (though it does not forbid it)
> >
> > could be argued against by the way SPARQL defines a dataset:
> >
> >> An RDF Dataset comprises one graph, the default graph, which does not
> >> have a name, and zero or more named graphs, where each named graph is
> >> identified by an IRI.
> 
> You are right. If taken literally, this definition [1] implies that an RDF Dataset can't have the same triples in the default graph and in a named graph. This clearly isn't the intention, so the wording is a bug in the SPARQL spec and needs to be fixed.
> 
> The formal definition [2] is fine.
> 
> (RDF graphs are set of triples. If two graphs contain the same triples, they are the same graph  they have no identity beyond the triples they contain.)
> 
> Best,
> Richard
> 
> [1] http://www.w3.org/TR/sparql11-query/#rdfDataset
> [2] http://www.w3.org/TR/sparql11-query/#sparqlDataset
> 
Received on Tuesday, 4 October 2011 05:06:03 GMT

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