W3C home > Mailing lists > Public > public-rif-wg@w3.org > April 2007

Re: bNodes as local constants

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Mon, 30 Apr 2007 16:40:25 +0000
Message-ID: <46361BE3.1090500@inf.unibz.it>
To: Dave Reynolds <der@hplb.hpl.hp.com>
Cc: Sandro Hawke <sandro@w3.org>, RIF <public-rif-wg@w3.org>






Dave Reynolds wrote:
> 
> Sandro Hawke wrote:
> 
>> My suggestion for RIF, I think, is that we say that RDF b-nodes should
>> be Skolemized for interoperation with RIF Core. 
> 
>>>> (1) This would be a possible way to go, yes.
>>>> (2) Another possibility would be to allow existentially quantified
>>>> variables in facts which come from RDF triples, and show that
>>>> skolemization can be used for reasoning.
>>>> (3) Finally, we could combine the two in a more modular way.  We could
>>>> define the combination of an RDF graph S with a set of rif rules P as a
>>>> tuple (S,P), and define a notion of combined interpretations,
>>>> similar to
>>>> what is done in DL-log [1].
>>>>
>>>> I think I would prefer the second option.   Compared to the first
>>>> option, it has the advantage that the embedding is closer to the actual
>>>> semantics of RDF.  Compared to the third option, it has the advantage
>>>> that (I think) it will be easier to understand, and you can more easily
>>>> be reused in extensions with nonmonotonicity and extensions towards
>>>> production rules.
>>> The second option is problematic. If we allow existential vars in the
>>> facts, then we have to revise the whole theory of rules starting with
>>> Horn. Every dialect will then need to be able to support existential
>>> facts,
>>> so it means that we will possibly need to revisit stable, well-founded,
>>> etc. semantics. These are possibly worthy things, but this group is not
>>> chartered with doing original research. Worse, if we do it wrong the
>>> first
>>> time and it becomes a W3C recommendation then future generations won't
>>> forgive us :-)
>>>
>>> I think option (3) is a safer way to go.
>>
>> It seems to me like option (1) is the safe/cheap route, since it doesn't
>> burden RIF implementors with RDF details.  
> 
> Agreed.
> 
> Our goal in integrating RIF with RDF should be to enable the use of RIF
> to interchange RDF processing rules such as ter Horst's R-entailment
> rules and the various use cases captured on the Wiki (and in turn
> implemented by systems such as CWM, Euler and Jena).
> 
> For all of those treating bNodes like skolem constants is, I believe,
> sufficient.
> 
> We certainly don't want to build RDF simple entailment into RIF.

As Michael pointed out, we already have RDF simple entailment through
non-ground query answering.

> 
> Whilst the DL+log approach may be appropriate for OWL/DL integration I
> fail to see what benefit it brings to RDF integration. The DL+log
> weak-safeness condition seems to rule out most of the RDF processing use
> cases.

I should have been more specific. I meant that we could use some general
semantic framework similar to the one used in DL+log; I did not mean to
propose to use specific syntactic restrictions such as weak safeness.


Best, Jos

> 
> Dave

-- 
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                         debruijn@inf.unibz.it

Jos de Bruijn,        http://www.debruijn.net/
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Received on Monday, 30 April 2007 20:12:27 GMT

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