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Re: more on RIF entailment regime

From: Axel Polleres <axel.polleres@deri.org>
Date: Thu, 25 Mar 2010 23:39:29 +0000
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <C0F395DA-E523-4116-A40C-21F825F208B9@deri.org>
To: Chimezie Ogbuji <ogbujic@ccf.org>
Hi Chime,

On 25 Mar 2010, at 14:24, Chimezie Ogbuji wrote:

> On 3/25/10 4:34 AM, "Axel Polleres" <axel.polleres@deri.org> wrote:
> > "Without appropriate safety conditions, cyclic references can rule out the
> > existence of a single intended Herbrand model of the combination and indeed
> > various stratification and stable model theories [STABLEMODEL] have been
> > defined in the literature that use a dependency graph to determine if a
> > ruleset is stratified and incorporate the restricted use of built-in function
> > symbols that allow the truth of a predicate to be well-defined by an external
> > procedure.  This entailment regime restricts the legal graphs to only those
> > that refer to strongly safe RIF core documents. This excludes the use of
> > negated (non-monotonic) atoms and cyclic references between terms in
> > built-ins."
> >
> > I think this paragraph might confuse. Stable models, stratification, etc. are
> > only vaguely related to the issue we face here, since they are usually only of
> > interest in the context of rule languages with (non-monotonic) negation.
> 
> The cyclic restrictions of stable models and stratification are of the same
> kind used in the RIF Core strong safety conditions (whether or not they are
> used for negation).

Well, it is inspired but quite different from that stratification, similar restrictions have been defined 
in terms of extending Datalog (with or without negation) with general function symbols... 
I just wouldn't give the stable model semantics as the primary reference here (besides that for stable model 
semantics I would use a different reference), AFAIR, stratification was first defined in terms of the perfect model semantics,
anyways...no?

>  This paragraph (and reference) was meant to describe
> how (traditionally) these kind of restrictions are used and how they are
> leveraged to ensure finiteness.

yes, but what I meant to say here is that in the current form it might be a bit distracting, that is why 
I'd rather keep these explaining sentences out, as e.g. referring to negation which is not at all in RIF
might be more confusing than enlightning here for the common reader. There is suficient explanation given 
in the RIF doc, IMO, which should suffice as reference, without adding a non-normative reference. Agreed?

best,
Axel

> 
> -- Chime
> 
> 
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Received on Thursday, 25 March 2010 23:40:08 GMT

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