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Re: finite approximation of the minimal Herbrand model for a RIF Core/BLD ruleset.

From: Axel Polleres <axel.polleres@deri.org>
Date: Wed, 24 Feb 2010 11:53:01 +0000
Cc: Jos De Bruijn <debruijn@inf.unibz.it>
Message-Id: <170A0505-AA38-4A80-9956-7E71028C614B@deri.org>
To: Sandro Hawke <sandro@w3.org>, Birte Glimm <birte.glimm@comlab.ox.ac.uk>, SPARQL Working Group <public-rdf-dawg@w3.org>
Note in that context that, another issue is the following:

RIF entailment is strictly speaking not only parametric to the dialect (Core/BLD/strongly safe core ... I hope we can define a unified entailmanet regime which catches all three) but also to the combination semantics chosen, cf. http://www.w3.org/TR/rif-rdf-owl/#Profiles_of_Imports, i.e. do we want to define only a RIF/Simple-Entailment regime, 
or also:

 RIF/RDF
 RIF/RDFS
 RIF/D
 RIF/OWL
 RIF/OWL DL
 RIF/OWL Full

(btw, the latter two have been renamed in the latest editor's draft in RIF, , cf. http://www.w3.org/2005/rules/wiki/SWC#Profiles_of_Imports,
due to comments form the OWL WG to
 RIF/OWL Direct
 RIF/OWL RDF-Based
)

To start with, I think my original proposal works straightforwardly for RIF/Simple, the others (particularly when we jump up to OWL) need more thought, and probably checking back with Jos & Birte ;-)
 

Axel


P.S.: <chairhat-off>I note that for my main use case, which is modeling different rule based approximations of fragments of the RDFS and OWL semantics in RIF, RIF/Simple is probably sufficient..</chairhat-off>


On 24 Feb 2010, at 11:38, Jos de Bruijn wrote:

> 
> >> On 2010-02-24 12:24, Axel Polleres wrote:
> >>> Below I forward some thought from jos on this with his consent:
> >>>
> >>> @jos: can you ealborate what exactly you mean here:
> >>>
> >>>> 2- the RDF(S) semantics gives you more than just blank nodes.
> >>>
> >>> in how far is this a (potential) problem?
> >>
> >> I'm not saying this is a problem per se. You were simply not taking the
> >> RDF(S) semantics (i.e., axiomatic triples & semantics conditions) into
> >> account in the definition you proposed.
> >
> > yes, this is another issue. good point.
> >
> >> Of course one needs to be careful with the infinite axiomatic triples,
> >> especially when considering query answering and not just checking
> >> entailment.
> >
> > A common way to deal with this in a finite approximation way is
> > a) ignoring (specifically the infinite) axiomatic triples alltogether
> > b) take only those from the infinite axiomatic triples (those about container membership properties)
> > that appear in the graph... I believe the latter is what we do in the current RDF(S) entailment regime, yes Birte?
> 
> b) seems to be the most reasonable way to go; but make sure to include
> at least one representative (for queries with blank nodes).
> Unnecessarily ignoring parts of the semantics (as in a) seems rather a
> bad idea.
> 
> 
> Cheers, Jos
> 
> >
> > Axel
> >
> >>
> >>
> >> Jos
> >>
> >>>
> >>> Axel
> >>>
> >>>
> >>>> ============================================================================
> >>>> On 2010-02-24 12:07, Axel Polleres wrote:
> >>>>>
> >>>>> On 24 Feb 2010, at 11:04, Jos de Bruijn wrote:
> >>>>>> On 2010-02-24 11:28, Axel Polleres wrote:
> >>>>>>> Hi Jos,
> >>>>>>>
> >>>>>>> Can you check this briefly and tell me whether I don't oversimplify
> >>>>>>> things here?
> >>>>>>
> >>>>>> I will have a more detailed look at it later on, but a few first comments:
> >>>>>> - you do not consider equality between data values, e.g.
> >>>>>> "1"^^int="1"^^decimal
> >>>>>
> >>>>> hmmm, I am at the moment, not sure how far this is a problem, but I definitly should include this in the issues!
> >>>>>
> >>>>>
> >>>>>> - I did not see how a minimal model for RIF-RDF combinations is defined,
> >>>>>> in particular I see no blank nodes or RDF(S) semantics
> >>>>>
> >>>>> ? Can't we just treat them as skolem constants? We are just interested in query answering...
> >>>>
> >>>> 1- if you treat blank nodes as skolem constants you need to say so.
> >>>> 2- the RDF(S) semantics gives you more than just blank nodes.
> >>>>
> >>>>> if you agree, I forward your comments to SPARQL, ok?
> >>>>
> >>>> Sure.
> >>>>
> >>>>
> >>>> Jos
> >>>
> >>>
> >>
> >> --
> >> Jos de Bruijn
> >>   Web:   http://www.debruijn.net/
> >>   Phone: +39 0471 016224
> >>   Fax:   +39 0471 016009
> >>
> >
> 
> --
> Jos de Bruijn
>   Web:   http://www.debruijn.net/
>   Phone: +39 0471 016224
>   Fax:   +39 0471 016009
> 
Received on Wednesday, 24 February 2010 11:53:37 GMT

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