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

From: Ivan Herman <ivan@w3.org>
Date: Mon, 15 Mar 2010 06:25:09 +0100
Message-ID: <4B9DC4B5.8080800@w3.org>
To: Chimezie Ogbuji <ogbujic@ccf.org>
CC: 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>, Jos de Bruijn <debruijn@inf.unibz.it>


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 05:24:38 GMT

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