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Re: shared bnodes (Skolems, SPARQL)

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Fri, 31 Aug 2012 14:29:04 +0100
Message-ID: <5040BC20.5020203@epimorphics.com>
To: Steve Harris <steve.harris@garlik.com>
CC: public-rdf-wg@w3.org

>>> <http://example.com/a> { _:a a <Foo> }
>>> <http://example.com/b> { _:a a <Bar> }

and also related ...

PREFIX : <http://example/>

INSERT DATA
{
   GRAPH :g1 { :s1 :p1 _:a }
   GRAPH :g2 { :s2 :p2 _:a }
}

followed by ...

SELECT * { GRAPH ?g { ?s ?p ?o } }

or

SELECT ?g1 ?g2 ?o {
   GRAPH ?g1 { ?s2 ?p2 ?o }
   GRAPH ?g2 { ?s2 ?p2 ?o }
}

>>>
>>> i.e. is there one bNode in two graphs, or two one in each graph.
>>
>> Exactly.   This is ISSUE-21 ("Can Node-IDs be shared between parts of a quad/multigraph format?")
>>
>> We could do a strawpoll on that here and now.
>>
>> My vote, not surprising anyone, would be:
>>
>> +1 (shared bnodes are needed for several use cases and are simpler than using Skolem nodes)
>
>
> -0.5 it's a significant change in behaviour for some systems, with unknown implications [would be -1 if Jena didn't do it already]
>
> We're not really big users of Trig, so I'd like to hear from people that are - if there aren't any big users of Trig, then I guess we probably should make the change, but I have to question why were bothering.

Jena and Sesame do the same thing as each other (TriG, NQuads, SPARQL 
Update)

Redland/rapper does not keep bnode labels across graphs in TriG apart - 
it simply copies the label across unchanged.

	Andy

>
> - Steve
>
Received on Friday, 31 August 2012 13:29:37 UTC

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