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Re: Scope of blank nodes in TriG?

From: Alex Hall <alexhall@revelytix.com>
Date: Fri, 14 Oct 2011 11:37:13 -0400
Message-ID: <CAFq2bizUrN3H__UFAFo4Bt5FZM+EHebRwLesmoOxr9NnLgyL+g@mail.gmail.com>
To: Ian Davis <ian.davis@talis.com>
Cc: RDF WG <public-rdf-wg@w3.org>
On Fri, Oct 14, 2011 at 5:45 AM, Ian Davis <ian.davis@talis.com> wrote:

> Example Document 3 in the TriG spec[1] shows the same blank node label
> being used in different graphs. My interpretation of the example is that
> those blank nodes are distinct, i.e. the scope of blank node labels is the
> graph not the TriG document. How do the main graph stores behave? Is it
> possible to put the same blank node into two different graphs? If so, this
> information would not be serializable in TriG if my interpretation is
> correct.
>

FWIW, Mulgara also allows graphs to contain blank nodes from other graphs in
the case where you update one graph with statements computed from a query
against another graph (inference graphs are one example).  For a while we
thought this was a bug; I would love to be told it's not since it's a useful
thing to have.

Question for the SPARQL folks: given the following sequence of operations:

INSERT DATA { GRAPH <g1> { _:s <p> <o> } }
INSERT { GRAPH <g2> { ?s <p> <o> } } WHERE { GRAPH <g2> { ?s <p> <o> } }

Does SPARQL take any position on whether the blank node inserted into g2 is
the same as or different from the one from g1?

-Alex



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> [1] http://www4.wiwiss.fu-berlin.de/bizer/trig/
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> --
> Ian Davis, Chief Technology Officer, Talis Group Ltd.
> http://www.talis.com/ | Registered in England and Wales as 5382297
>
Received on Friday, 14 October 2011 15:37:53 GMT

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