Re: bNodes as local constants

Jos de Bruijn <jos.debruijn@deri.org> wrote:
> 
> <snip/>
> 
> I do think that it is important to have a common definition for local
> names.  I was already afraid that at one point some people might think
> that local names are the same as bNodes :-)
> 
> I was not one of the big proponents of local names in the RIF, but I
> believe that the proponents (MichaelK, Hassan) share my definition, i.e.
> local names are not existentially quantified variables, but rigid constants.

Yes, local names have nothing to do with bNodes.
bNodes have logical meaning. Local names is just a twist to the naming schema.

> > My suggestion for RIF, I think, is that we say that RDF b-nodes should
> > be Skolemized for interoperation with RIF Core.  Other RIF dialects, if
> > they support general existential quantification, should not require
> > Skolemization.   Do you think that's good enough?
> 
> (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.


	--michael  


> Best, Jos
> 
> [1] Riccardo Rosati. DL+log: Tight integration of description logics and
> disjunctive datalog. In KR2006, 2006.
> 
> > 
> >      -- Sandro 
> > 
> > 
> 
>

Received on Friday, 27 April 2007 13:28:54 UTC