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Re: comments on RDF-Datasets-Proposal

From: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
Date: Wed, 29 Jun 2011 10:02:09 +0200
Message-ID: <4E0ADC01.1030608@liris.cnrs.fr>
To: "antoine.zimmermann@insa-lyon.fr" <antoine.zimmermann@insa-lyon.fr>
CC: "public-rdf-wg@w3.org" <public-rdf-wg@w3.org>
Antoine,

On 06/28/2011 12:07 PM, Antoine Zimmermann wrote:
> Pierre-Antoine,
> 
> Le 22/06/2011 19:19, Pierre-Antoine Champin a écrit :
>> Hi all,
>>
>> after today's telecon, I read the proposal at [1].
>>
>> First, it seems to be a "light" version of the Named Graph paper that
>> Pat mentionned. "Light", because it specifies that
>>
>> "The interpretation of the IRI [paired to graphs], in the RDF Semantics
>> sense, is left unspecified."
>>
>> It is all very well, but what happens when one wants to use those IRIs
>> *in* the named graphs? As proposed in the 'Semantic Extension' section
>> of [1]?
> 
> This section, which I wrote, was put there before we made any decision 
> on what the naming mechanism of graph store means. This section should 
> be considered informative, explaining how the basic semantics can be 
> extended. Such extension /may/ be defined externally to this WG.
> 
> The semantics is extremely simple and does not make any assumption on 
> what the "name of the graph" means. The graph name is just used as an 
> indice in a family of graphs.

I'm affraid you can not avoid to make that assumption. If I follow you,

  :G1 graph:imports :G2 .

would "only" mean

  the graph associated with URI :G1 imports the graph associated with
  URI :G2 (for some given association which is not *naming*)

Now assume that you know that

  :G2 owl:sameAs :G3 .

Nothing prevents you from infering now that

  :G1 graph:imports :G3 .

But the graph associated with URI :G2 may be completely different from
the graph associated with URI :G3 !

The problem comes from the fact that, to avoid the "graph naming
assumption", we need a property to talk about the URIs (and indirectly,
about the graph associated with them) while RDF properties always talk
about the resources denoted by the URIs.

If we used *resources* as graph identifiers, then it would be different.
But unfortunately, that is not what SPARQL is doing.

  pa



> 
> 
>>
>> Stating
>>
>>    :G1 graph:imports :G2
>>
>> does make some assumption about the meaning of :G1 and :G2 in the RDF
>> Semantics! More generally, if we want to make graphs first class
>> citizens of RDF, we need a mean to talk about them, hence we need IRIs
>> whose interpretation in RDF Semantics is that graph.
>>
>>    pa
>>
>>
>> [1] http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/RDF-Datasets-Proposal
>>
> 
> 
Received on Wednesday, 29 June 2011 08:02:43 GMT

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