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Re: A slight modification of your dataset proposal?

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Wed, 29 Feb 2012 19:34:41 +0100
Message-ID: <4F4E6FC1.7090302@emse.fr>
To: Ivan Herman <ivan@w3.org>
CC: W3C RDF WG <public-rdf-wg@w3.org>

Le 29/02/2012 18:49, Ivan Herman a écrit :
> Antoine,
> I was just wondering... we were discussing the relationships among
> different graphs in your setup, referring to the issue of, eg,
> functional property
> <g1>  { :john :age 23 } <g2>  { :john :age 33 } <g3>  { :age a
> owl:FunctionalProperty }
> in your semantics, the following setup does not really make a
> difference:
> <g1>  { :john :age 23 } <g2>  { :john :age 33 } :age a
> owl:FunctionalProperty.


> The last triple is in the default graph, which is just as well
> 'separated' from the individual named graphs. However... wouldn't it
> be more natural to say that the triples in the default graph are
> 'true' for all individual graphs? Ie, they give some sort of a
> universal truth, just as they are today.
> I guess your semantic definition could be modified quite easily by
> redefining the model:
> For (G, (<n1>,G1), (n2,G2), ..., (nk,Gk) ) a model is (I1, I2, ... ,
> Ik) where Ii is a model for Gi _and_ is also a model for G
> the rest is identical.
> Is this crazy?

It's not crazy, and at some point I thought this would make a lot of
sense, but during discussions earlier in 2011, people mentioned that a
number of SPARQL store are assuming that the default graph is actually 
entailing (or equivalent to, in some cases) the merge of all the "named" 
graphs. In order to accommodate this usage, I relaxed all the 
constraints on the default graph.

So, if you have a dataset where the behaviour is "default-as-merge", you 
can still define it as an extension of the dataset semantics by adding 
the constraints:

"the local interpretation of the default graph must satisfy all the RDF 
graphs in the dataset"

and if you prefer the "default-is-always-true" you can also express it 
in term of a semantic extension by adding what you say above.

Again, I think that these choices regarding which semantic extension is 
used could be specified in metadata about the dataset.

> Ivan
> ---- Ivan Herman, W3C Semantic Web Activity Lead Home:
> http://www.w3.org/People/Ivan/ mobile: +31-641044153 FOAF:
> http://www.ivan-herman.net/foaf.rdf

Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
Tél:+33(0)4 77 42 83 36
Fax:+33(0)4 77 42 66 66
Received on Wednesday, 29 February 2012 18:35:08 UTC

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