Re: bNodes as local constants

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.

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.

Dave
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Received on Monday, 30 April 2007 14:40:31 UTC