Re: RIF must cover RDF triples as data

Dave Reynolds wrote:
> 
> [[[
> *RDF Data*
> 
> RIF must cover RDF triples as data where compatible with Phase 1 semantics.
> 
> Specifically:
> 
> o RIF MUST provide a mapping from bNode-free RDF statements to RIF facts 
> so that RIF rules can be applied to (data derived from) RDF fact bases. 
> This MAY be a "natural" mapping in the sense that RDF facts are mapped 
> to ground instances of unary and binary RIF predicates or MAY be based 
> on a "holds" predicate.
> 
> This mapping will support the derivation of new RDF statements (i.e. 
> bNode-free RDF statements can be made in the head of rules).

I think that this is what confuses me. Granted, since some rules 
interchanged in RIF will apply to RDF data, such rules may contains 
statements that RDF triple XYZ holds, as a condition or as a conlusion 
of a rule; and thus, such statements need be representable in RIF 
(covered). Granted, they could be mapped in various way (btw, why isn't 
embedding RDF/XML an option?).

But I do not understand what using a "holds" predicate would add (I 
guess it is related to the semantics of a RDF triple, but how?).

And, above all, I do not understand the statement: "this mapping will 
support the derivation of new RDF statements". Why should RIF regulate 
what is allowed in the rules? Phase 1 semantics will allow atoms in the 
head, so atoms mapping to RDF statements will be allowed by RIF, if we 
have such a mapping. Whether or not there exist rule languages that are 
able to handle such rules is a different question (but if no such 
language exist, where would such rules come from? I mean, who would 
produce them?).

> Note that this RDF mapping will not imply any assumed implementation of 
> RDF-D-entailment or RDFS semantics, just RDF conjunctive assertion of 
> ground facts. There will be no assumed axiom base (in particular, no 
> assumed infinite axiom base of rdfs:ContainerMembership properties). 
> Applications wishing to employ RDFS semantics would need to include 
> appropriate RDFS axioms and closure rules explicitly.

Yep.

> o RIF MAY extend this mapping to include RDF statements involving 
> bNodes. At this point the working group reserves the right to defer 
> bNode handling to phase 2, to limit bNode usage to rule bodies only or 
> to approximate bNode semantics though the use of skolem constants.

Again, why wouldn't bNodes be allowed where they are compatible with 
phase 1 semantics (if there are such places)?

> o RIF MAY define an external predicate that will enable RIF rulesets to 
> query web-based SPARQL datasources.

You mean, using SPARQL queries to specifiy the range of rule variables 
when the rules are intended to apply to RDF data sources, for instance?

Christian

Received on Tuesday, 10 October 2006 14:53:16 UTC