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Re: Question about duplicate triples

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Tue, 31 Jul 2012 21:31:25 +0100
Message-ID: <5018409D.8020008@epimorphics.com>
To: David Booth <david@dbooth.org>
CC: public-rdf-dawg-comments@w3.org


On 31/07/12 21:26, David Booth wrote:
> On Tue, 2012-07-31 at 17:10 +0100, Andy Seaborne wrote:
>>
>> On 31/07/12 15:36, David Booth wrote:
>>> On Mon, 2012-07-30 at 18:18 -0400, David Booth wrote:
>>>> Suppose I LOAD a single file of NTriples into a named graph foo:, and
>>>> that file contains some duplicate triples such as:
>>>>
>>>>     _:bnode <http://example/ppp> <http://example/vvv> .
>>>>     _:bnode <http://example/ppp> <http://example/vvv> .
>>>>     _:bnode <http://example/ppp> <http://example/vvv> .
>>>>
>>>> According to the RDF Semantics, an RDF graph is a *set* of triples.
>>>> Hence, AFAIK the above file represents an RDF graph containing *one*
>>>> triple, and the graph is lean.
>>>>
>>>> If I then query that named graph as follows, how many solutions should I
>>>> get?
>>>>
>>>>     SELECT * WHERE { GRAPH foo: { ?s ?p ?v } }
>>>>
>>>> Is the SPARQL server permitted to return more than one solution (i.e.,
>>>> duplicates) in this case?
>>>>
>>>> I am aware of the DISTINCT keyword, but I always understood it as being
>>>> intended for situations where the query could generate multiple
>>>> candidate solutions, which is not the situation in this case.  It seems
>>>> a little weird if a SPARQL server might return multiple solutions in
>>>> this case, but would it still be conforming to the SPARQL spec if it
>>>> did?
>>>
>>> To further elaborate, if I issue this query in the above situation
>>>
>>>     SELECT (COUNT(*) AS ?count) WHERE { GRAPH foo: { ?s ?p ?v } }
>>>
>>> would any number greater than zero be a conforming result for ?count ?
>>>
>>> Or in a more general sense, if DISTINCT is not used, are the only
>>> semantically distinguishable values for COUNT: (a) zero; and (b) at
>>> least one?
>>
>> Please see
>>
>> http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2012Jul/0029.html
>
> Thanks, that answers my question.
>
>>
>> Please consider using the mailing list public-sparql-dev@w3.org for
>> general questions.  It allows for general discussion.
>
> Oh!  I didn't realize that I could post to that list.  I had previously
> tried to post to the RDF working group list, but found that only working
> group members are permitted to post to it, so I assumed the same to be
> true for the SPARQL working group.  Thanks for letting me know.

It is not the SPARQL working group list - it's an open (usual W3C 
subscription process) list for SPARQL users and developers.

	Andy

>
> David
>
>
>>
>> 	Andy
>>
>>>
>>>
>>>
>>
>>
>
Received on Tuesday, 31 July 2012 20:31:55 GMT

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