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Re: RDF named graph use case and requirement

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Wed, 21 Sep 2011 21:07:53 +0000
To: Graham Klyne <GK@ninebynine.org>
CC: W3C provenance WG <public-prov-wg@w3.org>, Andy Seaborne <andy.seaborne@epimorphics.com>
Message-ID: <EMEW3|c5a70e3d0041ef14a423e6a9dd866193n8KM8L08L.Moreau|ecs.soton.ac.uk|50E23168-CA53-4243-A691-6D3846CBFBF3@ecs.soton.ac.uk>
Hi Graham,

Why is this a requirement on named graphs and not on their metadata?

Didn't you want to encode

(by A and on d1) or (by B and on d2)

but you seem to have encoded it as 

(by A and on d1) and (by B and on d2)

which seems to allow the inference you describe. 

I think you have made the case for provenance to be put in a container (see latest spec). in this example you would need twoseparate containers, to avoid mix and match of provenance statements.

Professor Luc Moreau
Electronics and Computer Science
University of Southampton
Southampton SO17 1BJ
United Kingdom

On 21 Sep 2011, at 16:51, "Graham Klyne" <GK@ninebynine.org> wrote:

> (I've also posted this summary at http://www.w3.org/2011/prov/wiki/ProvenanceRDFNamedGraph#Requirement_from_discussion_with_Andy_Seaborne)
> In a meeting with Andy Seaborne this morning, we discussed provenance requirements and RDF named graphs, in light of some options that the RDF group might be considering.
> The resulting requirement that we articulated was that for the purposes of provenance, we must be able to treat two "named" graphs with identical graph content as two distinct entities.
> ...
> The use-case is this:
> Suppose we have some resource R.
> Observer A makes a provenance assertion about R on Monday 2011-09-19, which is expressed as an RDF graph Pra
> Observer B makes a provenance assertion about R on Friday 2011-09-23, expressed as RDF graph Prb
> To express provenance about the provenance assertions, we may wish to say:
> Pra statedBy A; onDate "2011-09-19" .
> Prb statedBy B; onDate "2011-09-23" .
> It may be that the provenance assertions Pra and Prb have identical content; i.e. they are RDFG graphs containing identical triple sets.  For the purposes of provenance recording, it is important that even when they express the same graphs, Pra and Prb are distinct RDF nodes.  If Pra and Prb are treated as a common RDF node, one might then infer:
> _:something statedBy A ; onDate "2011-09-23" .
> which in this scenario would be false.
> .....
> A particular consequence of this is that an RDF "named graph" specification based on graph literals (where RDF literals are self-denoting), somewhat like formulae in Notation 3, would have to be used with care.  That is, if Pra and Prb are graph literals, then Pra = Prb, and the given provenance-of-provenance statements could not be expressed as suggested above.
> (This does not preclude a graph literal approach being used, but the above use-case might need to be constructed slightly differently.)
> #g
> --
Received on Wednesday, 21 September 2011 21:09:01 UTC

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