Re: RDF and OWL compatibility

Dave Reynolds <der@hplb.hpl.hp.com> wrote:
> 
> Jos de Bruijn wrote:
> 
> > I think it is important to distinguish here between (a) rules with RDF
> > in the antecedent (body) and (b) rules with RDF in the consequent
> > (head). 
> > 
> > Rules of type (a) are relatively easy to deal with, both in a classical
> > setting and an LP setting.
> > 
> > Rules of type (b) could become a bit tricky, if we were to allow bnodes
> > and RDF vocabulary (as pointed out in the wiki).
> 
> Some of our use cases involve use of rules for RDF transformation and so 
> need RDF in the head, including RDF vocabulary (at least things like 
> rdf:type). So simply outlawing such rules doesn't seem like a viable option.
> 
> On the question of RDF vocabulary in the head, the only description on the 
> wiki of problems with that seems to be:
> 
> [[[
> However, here is the first case where the first treatment of RDF 
> meta-modelling becomes truely problematic. Consider, for example,
> 
>        p(c,a) .
>        q(c,b) .
>        rdfs:domain(X,Y) <- p(c,X), q(c,Y) .
>        a(d,e) .
> 
> where the two uses of a (as a constant and as a property) are interrelated. 
> It is possible to use a different treatment, employing a "holds" predicate, 
> but this is not particularly appealing.
> ]]]
> 
> That difficulty doesn't seem to arise with a triple(s,p,o) representation 
> or if a higher order syntax is available for expressing the RDFS closure 
> rules. Perhaps you/Peter could elaborate on the "not particularly 
> appealing" comment.
> 
> On the question of bNodes in the head, I hear the argument that it is not 
> sufficient to just treat these as new Skolem constants but my intuitive 
> understanding of the issue is too weak. It would be really helpful if 
> someone could construct a test case which demonstrates the difference in 
> results that arise between correct treatment of bNodes in the head versus 
> treatment as Skolem constants. In the concrete cases I've seen where bNodes 
> are used in the head of rules they seem to be intended as a form of 
> anonymous gensym - so the Skolem constant semantics may be the more 
> practically useful interpretation.

Exactly. This was precisely one of the points in our J. Data Semantics
paper,
http://springerlink.metapress.com/(xhvaac55xg4v2r55gzlnymfn)/app/home/contribution.asp?referrer=parent&backto=issue,4,9;journal,1019,2337;linkingpublicationresults,1:105633,1



	--michael

Received on Thursday, 5 January 2006 15:51:47 UTC