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Reconciliation of concerns, re islands and dataset semantics?

From: Ivan Herman <ivan@w3.org>
Date: Thu, 1 Mar 2012 10:27:06 +0100
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>, Pat Hayes <phayes@ihmc.us>, W3C RDF WG <public-rdf-wg@w3.org>
Message-Id: <6A1D6E01-7778-4FC7-BA66-676FA7239B70@w3.org>
Guys,

I do not claim to have read and understood all the details of your discussion. I hope I have grasped the essential aspects of it, though. And I was wondering whether it was possible to reconcile Antoine's proposal (that do have some attraction for my engineering mind, I must admit) and Pat's objections. Let me try to give an alternative to Antoine's definition, and see if that works.

An interpretation 'I' of a Graph is a function which abides to certain semantic conditions. If there is a graph 'G', it is therefore possible to talk about 'I|G', ie, the restriction of the function to 'G'. With that in mind:

Let D = (G, (<n1>,G1), (<n2>,G2), ... , (<nk>,Gk))

and let 'I' be a mapping, ie, and interpretation, from 'union(G,G2,G2,...,Gk)' such that, 'I|G', 'I|G1', ... , 'I|Gk' are all RDF/RDFS/OWL Full etc. interpretations (ie, they abide to the semantic condition locally).

If 

E =  (H, (<m1>,H1), (<m2>,H2), ... , (<mk>,Hk))

is another dataset, than we can say that 'D' entails 'E' if for all interpretations 'I' of 'D', 

'I|H', 'I|H1', ... , 'I|Hk'

are all interpretations, which seems to be the same as saying that 'I' is also an interpretation of 'E'.

This means that there is level of consistency shared by all graphs in a dataset, ie, if a resource 'R' is in 'G1' and 'G2', then we are sure that an interpretation maps it identically, because 'I' is defined as a mapping on the *union* of all graphs. But the semantic conditions, as well as the entailments, are restricted to the individual graphs.

Can that work?

This approach, if again it works, seem to be a much less radical change, both conceptually and practically, to the current RDF standards. Therein lies, for me, its attraction...

Two more things.

1. A variant, that I touched upon in a mail to Antoine yesterday evening, is to say that 'I' must be interpretations of 'I|union(G,G1)', etc. Ie, 'G', the default graph, contains "universal" truths. As Antoine says, this may be a parametrization of the dataset itself, because this may be too much to ask in some cases. To be seen (for me, I must say, this universal truth approach sounds more natural)

2. I would note that neither this approach nor Antoine's, nor, in fact (I believe) Pat's quad approach touches upon the other discussion on named graphs that we are having, namely the exact relationships between '<ni>' and 'Gi'. In these semantic approaches the uri-s merely serve as classifiers. Whether we have some GET Semantics or SameAs semantics or whatever attached to '<ni>' and it corresponding 'Gi' is to be defined separately. Semantically, what this means that the default graph, ie, 'G', may include some additional

(ni, rdf:type, rdf:GETSemanticsClass) 

triples, but where the 'semantics' will not be expressed in terms of semantic conditions. Which I think is fine with me, just wanted to make it clear and it may be worth separating the two discussions in the group explicitly...

Now is my turn to be torn apart by Pat:-)

Ivan

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Ivan Herman, W3C Semantic Web Activity Lead
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Received on Thursday, 1 March 2012 09:27:11 GMT

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