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Re: New Proposal (6.1) for GRAPHS

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 28 Mar 2012 14:53:45 +0100
Message-ID: <4F7317E9.6030702@epimorphics.com>
To: public-rdf-wg@w3.org


On 28/03/12 12:18, Steve Harris wrote:
> 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.

In the example of:

<u1>  {<a>  <b>  <c>  }

as an inference of some kind? (rdf:GraphLabel)

In:

    { <u2> a rdf:Graph }
    <u2> { <a> <b> <c> }

the base data includes the match to that pattern.

(modulo the union graph thing but this is loading the default graph 
explicitly -- what happens in such systems when the data explicitly says 
"default graph"?)

	Andy



>
> 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)
>>
>>
>
Received on Wednesday, 28 March 2012 13:54:21 GMT

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