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Re: Some Embedding necessary for RIF-Simple - Was Re: [TF-Ent] RIF Core Entailment section

From: Jos de Bruijn <jos.debruijn@gmail.com>
Date: Mon, 15 Mar 2010 08:20:14 +0100
Message-Id: <9FB81A81-5EE3-413B-9D6E-30F6C77BA16F@gmail.com>
To: Ivan Herman <ivan@w3.org>
Cc: Chimezie Ogbuji <ogbujic@ccf.org>, Birte Glimm <birte.glimm@comlab.ox.ac.uk>, SPARQL Working Group WG <public-rdf-dawg@w3.org>, Axel Polleres <axel.polleres@deri.org>, Sandro Hawke <sandro@w3.org>
Ivan,

I can confirm that your basic intuition about the combinations is  
correct.
Chime may not have fully understood the RIF model theory. RIF does not  
have a minimal model semantics; it has a standard first-order style  
model theory.
Let's consider the empty RIF document R. Since it is empty, there are  
no constraints on the models, and so every RIF interpretation is a  
model of R, in particular also every interpretation that satisfies the  
formula :a#:b.
If we now look at combinations of R with the graph S={:a a :b. } we  
have that only RIF structures I that satisfy :a#:b can be part of  
common models. Certainly, such structures I satisfy R, and so the  
combination is satisfiable.

Cheers, Jos

-- sent from my PDA

On 15 Mar 2010, at 06:25, Ivan Herman <ivan@w3.org> wrote:

>
>
> On 2010-3-15 01:48 , Chimezie Ogbuji wrote:
>> Ivan,
>>
>> On 3/13/10 5:19 AM, "Ivan Herman" <ivan@w3.org> wrote:
>>> Chime,
>>> I do not understand...
>>
>> Okay, I'll see if I can help with that.  I've sent Jos a separate  
>> email
>> about this as well.
>>
>>> On 2010-3-12 21:10 , Chimezie Ogbuji wrote:
>> ..snip..
>>> My understanding of the proposed semantics (by Axel) for  
>>> rif:imports is
>>> that this combination is transformed as follows:
>>>
>>> 1. Starting point
>>> G: _:a rdf:type _:b .
>>>   <> rif:imports <R> .
>>> R: empty
>>>
>>> 2. Apply the semantics
>>> G': _:a rdf:type _:b
>>> R': Import(G, <http://www.w3.org/2007/rif-import-profile#Simple>)
>>>
>>> (whether the <> rif:imports <R> is removed from G is still an open
>>> question but does not seem to influence this issue)
>>
>> Okay, but independent of how rif:imports is interpreted (for a lack  
>> of a
>> better word), the SG still only has one triple relevant to RIF-simple
>> entailment, right?:
>>
>> _:a rdf:type _:b
>>
>>> 3. From the RIF point of view, that is equivalent to:
>>> R'' : _a # _b .
>>>
>>> (using RIF's unique id-s which look very much like skolemization  
>>> to me).
>>
>> Okay, this is the point where the issue comes in.  I'm not sure  
>> what you
>> mean by 'from the RIF point of view', because - as I understand it -
>> entailment does not involve any RIF interpretation of the RDF graph  
>> (which
>> is the reason why we need to embed the triples from the scoping  
>> graph into
>> the RIF document in order to interpret them using RIF semantics).
>>
>
> This is the crucial point and I think you did the best thing by asking
> Jos on this, and there might indeed be a terminological/editorial  
> issue
> in the RIF-RDF document (and it is the right time to signal this if
> there is!).
>
> My mental model of the RIF-RDF combination has always been that when a
> RIF rule set 'imports' an RDF graph, than this means as if all triples
> were effectively defined in terms as RIF frames. Ie, the import will
> definitely create the following:
>
> _a[rdf:type->_b]
>
> furthermore, the definition of the common interpretation with the 10
> rules puts an extra set of correspondence on how to 'see' the RDF
> triples through a RIF glass. Ie, in my mind, that means that the RIF
> entailment part operates on the single rule
>
> _a # _b .
>
> If true, this means that your issue below becomes moot. If false,  
> than I
> am not sure any more how this common thing works...
>
> So Jos, you are the source of all wisdom!
>
> Ivan
>
>
>
>> So, at this point (i.e., before 3 above) we form the following  
>> combination:
>>
>> <Rempty,G''>
>>
>> Where G'' is sk(G'):
>>
>> <unique-URI-1> rdf:type <unique-URI-2> (lets refer to this triple  
>> as t1)
>>
>> The problem is that there is no (simple) interpretation for G'' in  
>> which
>> IEXT(IS(rdf:type)) is empty.  Since, G'' is ground, we know I(t1)  
>> is true
>> and that IEXT(IS(rdf:type)) must not be empty (from what tr/rdf-mt  
>> says
>> about how simple entailment interprets ground RDF graphs in 1.4).
>>
>> Since Rempty is empty, I_truth(I_isa(a,b))= false, and by the  
>> wording of
>> condition 7, IEXT(IS(rdf:type)) must be empty.  However, above we  
>> see that
>> it can't be empty.
>>
>>> Do I severely miss something here?
>>> Actually, if what you say was true, then I think there is a  
>>> problem in
>>> the RIF-RDF document. That has to be signalled to the RIF group
>>
>> I'm not sure if this necessarily indicates a problem with the RIF-RDF
>> document (hopefully Jos can speak on this) but perhaps suggests  
>> that the
>> embeddings (or at least some of them: Simple and RDF for example)  
>> should be
>> made normative since implementations cannot practically implement  
>> RIF-RDF
>> entailment without them.  Or at least, a simple paragraph  
>> emphasizing the
>> counter-intuitive behavior of combinations where there is not  
>> already a
>> correspondence between triples, frames, and their terms.
>>
>> -- Chime
>>
>>
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>
> -- 
>
> Ivan Herman, W3C Semantic Web Activity Lead
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Received on Monday, 15 March 2010 08:26:37 GMT

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