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Re: New Proposal (6.1) for GRAPHS

From: Steve Harris <steve.harris@garlik.com>
Date: Wed, 28 Mar 2012 12:18:48 +0100
Cc: public-rdf-wg <public-rdf-wg@w3.org>
Message-Id: <1BCCAE03-53FC-4348-81D8-9CCEFBFD306E@garlik.com>
To: Sandro Hawke <sandro@w3.org>
This seems good to me, assuming that the TriG docs below will have their current behaviour in SPARQL systems when imported, i.e.

SELECT ?type
WHERE {
   ?g a ?type .
   GRAPH ?g { <a> <b> <c> }
}

Will return rdf:Graph.

The only reservation I have is relating to systems where (out of the box) the default graph is the Union of the named graphs - this is relatively common. If the TriG also has:

<u3> { <u2> a foaf:Person }

Then the answer to the above query would be ?type = rdf:Graph, foaf:Person - which is not what was intended.

In 4store, for example, you could force the issue by instead asking:

SELECT ?type
WHERE {
   GRAPH <default:> { ?g a ?type }
   GRAPH ?g { <a> <b> <c> }
}

but that's not standard SPARQL, uses a system specific ugly URI, and is probably semantically dubious.

- Steve

On 28 Mar 2012, at 03:23, Sandro Hawke wrote:

> I've written up design 6 (originally suggested by Andy) in more
> detail.  I've called in 6.1 since I've change/added a few details that
> Andy might not agree with.  Eric has started writing up how the use
> cases are addressed by this proposal.
> 
> This proposal addresses all 15 of our old open issues concerning graphs.
> (I'm sure it will have its own issues, though.)
> 
> The basic idea is to use trig syntax, and to support the different
> desired relationships between labels and their graphs via class
> information on the labels.  In particular, according to this proposal,
> in this trig document:
> 
>   <u1> { <a> <b> <c> }
> 
> ... we only know that <u1> is some kind of label for the RDF Graph <a>
> <b> <c>, like today.  However, in his trig document:
> 
>   { <u2> a rdf:Graph }
>   <u2> { <a> <b> <c> }
> 
> we know that <u2> is an rdf:Graph and, what's more, we know that <u2>
> actually is the RDF Graph { <a> <b> <c> }.  That is, in this case, we
> know that URL "u2" is a name we can use in RDF to refer to that g-snap.
> 
> Details are here: http://www.w3.org/2011/rdf-wg/wiki/Graphs_Design_6.1
> 
> That page includes answers to all the current GRAPHS issues, including
> ISSUE-5, ISSUE-14, etc.
> 
> Eric has started going through Why Graphs and adding the examples as
> addressed by Proposal 6.1:
> http://www.w3.org/2011/rdf-wg/wiki/Why_Graphs_6.1
> 
>     -- Sandro (with Eric nearby)
> 
> 

-- 
Steve Harris, CTO
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Received on Wednesday, 28 March 2012 11:19:11 GMT

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