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Re: why I don't like default graphs in the DATASET proposal

From: james anderson <james.anderson@setf.de>
Date: Tue, 4 Oct 2011 12:17:18 +0200
Message-Id: <98D3143C-7CC6-4247-8FF6-396B85B0FDBB@setf.de>
To: SPARQL Comments <public-rdf-dawg-comments@w3.org>
good morning;

On 2011-10-04, at 11:05 , Richard Cyganiak wrote:

> Hi Axel,
>
> On 4 Oct 2011, at 06:05, Axel Polleres wrote:
>>>>> An RDF Dataset comprises one graph, the default graph, which  
>>>>> does not
>>>>> have a name, and zero or more named graphs, where each named  
>>>>> graph is
>>>>> identified by an IRI.
>>>
>>> You are right. If taken literally, this definition [1] implies  
>>> that an RDF Dataset can't have the same triples in the default  
>>> graph and in a named graph. This clearly isn't the intention, so  
>>> the wording is a bug in the SPARQL spec and needs to be fixed.
>>
>> I don't see how the wording at [1] would imply disjointness of the  
>> named and default graphs.
>> Since a *named graph* is a *pair* of a graph and its name (as  
>> indeed made more explicit in [2]),
>> any named graph is per definition different from the default graph  
>> or from any other named graph, so
>> I don't think that the wording  at [1] is buggy.
>
> If there's a named graph <u1,G1>, then it is reasonable to say that  
> “G1 has the name u1”, because G1 is paired with a graph name u1.
>
> If one accepts “G1 has the name u1” as a true statement, then it  
> follows that G1 cannot be the default graph, because [1] states  
> that “[the default graph] does not have a name”.
>
> I agree that [2] is unambiguous. The problem is that [1] can be  
> easily read as implying something that isn't true according to [2],  
> as has happened here in RDF-WG.
>
> Best,
> Richard
>
>
>
>>
>> best regards,
>> Axel

the wording of the cited passage from section 13[1] is perfectly  
clear to this reader as it stands. while it would be possible to draw  
the conclusion suggested by the second sentence, above, that "it  
follows that G1 cannot be the default graph", this would require that  
the two graphs denoted by G and G1 were not permitted to have the  
same constituent statements because some dataset definition  
designated them with distinct identifiers. nothing in the document  
either states or implies that.

example 2 of section 13 more likely implies just the opposite with  
respect to disjointness. if one reduces the example, to eliminate the  
named graph <http://example.org/alice> from the dataset, it makes  
clear that the designator for a graph in the context of a dataset  
declaration implies nothing about the graph's constituent statements.


>>> [1] http://www.w3.org/TR/sparql11-query/#rdfDataset
>>> [2] http://www.w3.org/TR/sparql11-query/#sparqlDataset
>>>
>>
>
>
Received on Tuesday, 4 October 2011 10:17:51 GMT

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