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Re: shared bnodes (Skolems, SPARQL)

From: Sandro Hawke <sandro@w3.org>
Date: Fri, 31 Aug 2012 12:30:52 -0400
Message-ID: <5040E6BC.2000504@w3.org>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
CC: Steve Harris <steve.harris@garlik.com>, public-rdf-wg@w3.org
On 08/31/2012 09:29 AM, Andy Seaborne wrote:
>
>>>> <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 }
> }
>

Indeed.

Are those currently SPARQL 1.1 test cases?  [1]   Is it clear what the 
answer is in SPARQL 1.1?

       -- Sandro


[1] I don't see anything like that in 
http://www.w3.org/2009/sparql/docs/tests/data-sparql11/basic-update or 
nearby, but maybe some tests are somewhere else...?

>>>>
>>>> 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 16:31:06 UTC

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