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Re: Reconciliation of concerns, re islands and dataset semantics?

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Thu, 01 Mar 2012 13:31:48 +0100
Message-ID: <4F4F6C34.3070705@emse.fr>
To: Ivan Herman <ivan@w3.org>
CC: Pat Hayes <phayes@ihmc.us>, W3C RDF WG <public-rdf-wg@w3.org>
Le 01/03/2012 13:05, Ivan Herman a écrit :
>
> On Mar 1, 2012, at 12:42 , Antoine Zimmermann wrote:
>
> [...]
>
>> If such is your proposal, then it's viable in the sense that it can
>> work as a logic, but I'm wondering how this would solve the
>> endorsement/beliefs/provenance/temporal use cases.
>>
>
> My understanding of the discussion is that, in your case, what
> happens is that if there is a resource (URI) that appears in both G1
> and G2, the respective interpretations (or models) may be different
> on that resource, depending on whether you use the interpretation for
> G2 or G2. This is the issue I want to take away, while still keeping
> the graphs separate

Yes. The interpretation of a URI is contextual. Note that it's like the 
interpretation of the word "graph", which in some context means a pair 
of sets (V,E), in other contexts it means a set of triples.

>>>
>>> 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'.
>>
>> I guess here you mean "model" rather than interpretation (i.e., an
>> interpretation that satisfies the dataset).
>
> Sorry. I did refer to the fact that the interpretation abides to the
> semantic conditions of RDF(S) et al, I guess that is the same. (RDF
> Semantics does not use the term 'model', only rdf-interpretation,
> rdfs-interpretation, etc...)

Looking at the specs again, I understand why the term "model" is not 
used (in that sense): see http://www.w3.org/TR/rdf-mt/#glossModeltheory

>
>> Said otherwise, entailment is defined "as usual":
>>
>> D entails E iff all models of D are models of E.
>>
>
> I guess that is correct
>
>> (Pat just reminded me in his last email that I do not use the
>> "usual" definition of entailment in the dataset proposal, but I'm
>> gonna fix this).
>>
>>
>>> 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 certainly works as a logic, but the question is whether it
>> addresses the use cases dealing with multiple graphs. Take the case
>> when I want to have the following information:
>>
>> :x thinks that { :a owl:sameAs :b } :y thinks that { :a
>> owl:differentFrom :b }
>>
>> which could be reformulated in :x endorses the first graph, :y
>> endorses the other graph, or the document at :x contains the first
>> graph, the one at :y contains the second, or again, a SPARQL
>> dataset contains the two graphs respectively "named" :x and :y.
>>
>
> If (:a owl:sameAs :b) and (:a owl:differentFrom :b) appeared in the
> same graph, then an OWL reasoner, using the definition of the
> predicates, would deduce that there is a inconsistence. I mean: the
> triples themselves are just fine, it is up to a reasoner to find the
> problem.
>
> If they are in different graphs, then the inconsistence would not
> occur, because we only care about the models in separate graphs,
> independently from one another.

Hmm, this seems to contradict what you said above. If URIs are 
interpreted identically in all graphs with overlapping vocabularies, how 
can :a be interpreted as the same thing as :b and at the same time as 
something different then :b? Either you have an inconsistency, or you 
interpret the URIs differently in the two graphs.

> [...]
>
>>
>> Now, if you want to do temporal reasoning, provenance, trust, it's
>> more complicated. But the fierceful rejection by Pat on the mere
>> idea of a multi-interpretation semantics has deviated the
>> discussion away from these issues.
>
> And I do not think this working group should deal with temporal
> reasoning, provenance, or trust. Just giving the basis in terms of
> that semantics is what should be done.

I do not mean the WG should provide a standard for temporal reasoning 
etc. I just mean that we have to analyse these use cases in light of the 
various options we have for defining a semantics of 
datasets/quads/multiple-graph structure.

 > [...]
>>
>> True, but this is difficult to put in the formal semantics as model
>> theory is only interested in what is true from a given logical
>> theory. It does not normally deal with behaviour, what an
>> application should *do*. That is why owl:imports does not have a
>> particularly constraining model theoretic semantics. The mechanism
>> behind owl:imports is defined outside the semantic documents.
>
> I *think* I understand what you say, and it does not seem to
> contradict what I said: what, say, rdf:GETSemanticClass means is
> defined outside the model theoretic semantics. That is what I meant
> at least.

Then we are on the same page. Good.

>
> Ivan
>
>>
>> Similarly, we can very well define mechanisms that have no
>> representation in terms of model theory.
>>
>>
>>> Now is my turn to be torn apart by Pat:-)
>>
>> Good luck ;)
>>
>>
>> AZ
>>
>>>
>>> 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 France Tél:+33(0)4 77 42 83 36
>> Fax:+33(0)4 77 42 66 66 http://zimmer.aprilfoolsreview.com/
>>
>
>
> ---- 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
France
Tél:+33(0)4 77 42 83 36
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/
Received on Thursday, 1 March 2012 12:32:19 GMT

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