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Re: RDF named graph use case and requirement

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 21 Sep 2011 15:27:28 -0700
To: Graham Klyne <GK@ninebynine.org>, public-rdf-prov@w3.org
Cc: W3C provenance WG <public-prov-wg@w3.org>, Andy Seaborne <andy.seaborne@epimorphics.com>
Message-ID: <1316644048.21708.17.camel@waldron>
[cc'ing public-prov-wg, but reply-to set to public-rdf-prov, where as I
understand it this discussion should proceed.]

On Wed, 2011-09-21 at 16:49 +0100, Graham Klyne 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 

( quiet grumble about the use of the undefinable term "named graph"... )

> 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.

Isn't this just some modeling confusion?  Pra and Prb are each an event
of the authoring of a statement (ie they are "statings"), not
statements, based on how you use them, giving them dates and such.
Those two statings can then be connected to the same statement (graph,
Pra statement G1; dc:creator A; dc:date "2011-09-19".
Prb statement G1; dc:creator B; dc:date "2011-09-23".

Then G1 can just be a literal, or whatever we use to allow conversations
about g-snaps.

> .....
> 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.

It seems to me Pra and Prb are not g-snaps (RDF graphs), so there's no
problem here.

     -- Sandro

> (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 22:27:45 UTC

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