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Re: more on RIF entailment regime

From: Chimezie Ogbuji <ogbujic@ccf.org>
Date: Fri, 26 Mar 2010 09:46:50 -0400
To: "Axel Polleres" <axel.polleres@deri.org>
cc: "SPARQL Working Group" <public-rdf-dawg@w3.org>
Message-ID: <C7D2330A.10888%ogbujic@ccf.org>
On 3/25/10 7:39 PM, "Axel Polleres" <axel.polleres@deri.org> wrote:
>> 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?

The reference I chose wasn't meant to suggest that stable models are the
progenitor of this method.  I chose that reference because it gives a good
overview of the background.  Do you have a suggestion for a different one?

>>  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.

I could remove mention of negation (see the sentence below), but my
intention was to clarify that even though stratification techniques were
mainly motivated by being able to address non-monotonic semantics, they are
applicable to positive programs as well.

"..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."

> There is 
> suficient explanation given
> in the RIF doc, IMO, which should suffice as reference, without adding a
> non-normative reference. Agreed?

Actually, (from an implementors perspective) I don't feel like there is
sufficient explanation of the intuition behind the strongly safe criteria
and this is made worse in some ways by the fact that those criteria are only
informative in that document.

-- Chime


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Received on Friday, 26 March 2010 13:47:37 GMT

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