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Re: Another try.

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Wed, 22 Feb 2012 11:05:19 +0100
Message-ID: <4F44BDDF.2060707@emse.fr>
To: public-rdf-wg@w3.org
Pat,

Le 21/02/2012 23:23, Pat Hayes a écrit :
>
> On Feb 21, 2012, at 10:00 AM, Andy Seaborne wrote:
>
> [skip]
>
>>
>> All existing vocabularies like FOAF don't say anything about
>> P(S,O,G) so if we just do it as an extension from pairs to triples
>> (triples to quads), then the existing definitions that talk about
>> pairs don't apply any ore do they?
>>
>> Concretely:
>>
>> :g1 {<x>  foaf:age 15 }
>>
>> :g2 {<x>  foaf:age 25 }
>>
>> In a graph foaf:age has a definition (albeit troublesome)..
>
> Right now, this datastore contains a contradiction

It depends on what you mean by "contains". Here, you are assuming
implicitely that a dataset "contains" the merge of the RDF graphs inside
the "named" graphs. It's like assuming that a set of numbers "contains"
the sum of the numbers. In a way it is true, since if I have 5 bags,
each of which contains 5 coins, then I can say that my bags contain 25
coins.

But I do not think this is what is at stake here. I think what's
important is:
  1) what can I do with this dataset?
  2) what can I infer?
  3) is it inconsistent?

Right now, what we have is an answer to 1) via the SPARQL specs, which
define what answers one can get to a query over a dataset. We do not
have an answer to 2) and 3) yet because we do not have a formal
semantics for datasets (contrary to what you said in an email a while
ago). What you propose with the quad-graph semantics is technically a
semantics for datasets, even though you base it on quads for convenience.


AZ.


BTW: even with a merge in the example dataset, there is no 
contradiction, formally speaking, but it's just anecdotal.




 > (well, assuming global scope of bnodes, but leave that issue aside.).
 > If we adopt the proposal it still does, but if we instead write it as
>
> :g1 {<x>  foaf:age 15 + )
>
> :g2 {<x>  foaf:age 25 + }
>
> then its no longer a contradiction. Presumably, that age was recorded
> at different times, or under different circumstances, and the :g1/2
> URIs encode these differences somehow, since they have now been
> treated as a genuine parameter of the foaf:age relation.
>
> Pat
>
>>
>>> Does this connect to SPARQL's idea of a default graph in a useful
>>> way?
>>
>> Wasn't on my mind as such.
>>
>>>
>>> -w
>>
>> Andy
>>
>>
>
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-- 
Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
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France
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Received on Wednesday, 22 February 2012 10:05:46 UTC

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