- From: Sandro Hawke <sandro@w3.org>
- Date: Fri, 27 Apr 2007 10:21:35 -0400
- To: kifer@cs.sunysb.edu (Michael Kifer)
- Cc: Jos de Bruijn <jos.debruijn@deri.org>, RIF <public-rif-wg@w3.org>
> > 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
Can you give me one or more example that show this? Like, if I were
writing a translator from RIF Core to some FOL, how would I translate
local names, and IRIs, and how would merging work?
> > (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. Doesn't (3) mean that every
RIF Core implementation has to implement RDF semantics -- ie bNodes?
- Sandro
Received on Friday, 27 April 2007 14:22:36 UTC