Re: Importing RDF documents from RIF - part 2

I realise I never followed up on that...

On 19 Jan 2010, at 16:09, Jos de Bruijn wrote:

> 
> On 2010-01-19 16:47, Axel Polleres wrote:
> > FWIW, the semantics of owl:imports is defined by OWL as well, plus  they have defined an
> > RDF serialisation, and that makes perfect sense to me, if I look at it from the
> > So, I can't really follow the argument why this would be in the scope of RDF.
> 
> I'm not saying it is. I'm just saying it's an extension of RDF, and thus
> seems out of scope for RIF.
> OWL 2 DL defines an RDF serialization, which does not have much to do
> with the RDF semantics. OWL 2 Full is an extension of RDF.
> 
> >
> >>  think it would be better to refer to the RIF ruleset
> >> from the SPARQL query, and have the RIF ruleset import the RDF dataset.
> >
> > there is no way to do this directly, I mean without changing the definitions of
> > BGP extensions, that is at the heart of the definition of entailment regimes for SPARQL.
> 
> I don't really understand the difference from the point of view of
> SPARQL between RIF importing RDF and RDF importing RIF.
> Why does "RDF importing RIF" not require changing the definition of BGP
> extensions, while "RIF importing RDF", considering that the proposed
> semantics are the same?

BGP matching is entirely defined in terms of an RDF dataset, if you can't refer 
from that dataset to the RIF ruleset, that's a problem.

> >
> > I agree with the concern that it might be too late for  RIF to squeeze that in the current specs,
> > it'd be great though, if we'd get a WG note out at least. If only its to endorse that we'd use
> > the URI rif:usedWithProfile?
> >
> > Since OWL has defined an RDF serialisation, handling that from SPARQL is
> 
> I guess this sentenced was cut off?
> 

yes... the missing word was "easy", meaning to say handling OWL from SPARQL is easy, since the OWL ontology is 
encoded in the RDF graph. 

> >
> >> By the way, I would be very interested in the semantics you have in mind
> >> for the SPARQL queries on RIF ruleset.
> >
> > For very limited rulesets (strongly safe) and simple RDF its fairly straightforward,
> > since the closure is finite, finiteness of answers to conjunctive queries (i.e. BGP matching)
> > should be straightforward. I am unsure whether we'd get to any more complex combinations,
> > i.e. mixing OWL/RDFS, etc. plus rulesets, this might also depend on how the resp
> > OWL, RDFS, etc. entailment regimes evolve in SPARQL.. feedback welcome at [1], though you may
> > want to wait for the next pub round which is pending (next week hopefully).
> 
> I would be interested in your definition of "closure".

As I said, the closure is finite for strongly safe core (minimal Herbrand model, definiable 
by the common least fixpoint operator).

> It is not in the
> mentioned spec. I am particularly concerned about how blank nodes are
> treated. When not being careful, the closure is infinite, even for very
> simple graphs and empty rulesets.

in what sense are blanknodes a problem? (when thinking only of strongly safe RIF Core?)
What speaks against just treating them as skolem constants? That's, BTW also what we do in the 
OWL entailment regimes in SPARQL already.

Axel

> 
> 
> Cheers, Jos
> 
> >
> >
> > Axel
> >  
> > 1. http://www.w3.org/TR/sparql11-entailment/
> >
> > On 19 Jan 2010, at 15:07, Jos de Bruijn wrote:
> >
> >> This sounds like a reasonable extension of the RDF semantics. Not
> >> convinced, though, that this is in the scope of the RIF-RDF+OWL spec.
> >> For this reason, and for procedural reasons, I suggest that if such an
> >> extension of RDF is of wider interest, a separate spec be written for
> >> this extension.
> >>
> >> Furthermore, I am not convinced that extending RDF is the best solution
> >> to your problem of querying RIF-RDF combinations using SPARQL: RIF is
> >> "on top of" RDF. I think it would be better to refer to the RIF ruleset
> >> from the SPARQL query, and have the RIF ruleset import the RDF dataset.
> >>
> >> By the way, I would be very interested in the semantics you have in mind
> >> for the SPARQL queries on RIF ruleset.
> >>
> >>
> >> Cheers, Jos
> >>
> >> On 2010-01-19 15:55, Axel Polleres wrote:
> >>> Here the easy-to-digest version:
> >>>
> >>> In order to enable the import of RIF documents from RDF, I suggest the addition of a new section
> >>> 6 (or alternatively a new subsection to section 5) to
> >>> http://www.w3.org/2005/rules/wiki/SWC#Semantics_of_RIF-RDF_Combinations
> >>> which essentially says the following:
> >>>
> >>> ====================================================================================
> >>>
> >>> = 6 Importing RIF rulesets in RDF =
> >>>
> >>> The models of a RIF-X-combination (R,S) where any of the graphs in S contains a ground triple
> >>>
> >>>    R1 rif:usedWithProfile P .
> >>>
> >>> such R1 is an IRI referring to a RIF document and P is a URI referring to an imports profile as defined in
> >>> Section http://www.w3.org/2005/rules/wiki/SWC#Profiles_of_Imports
> >>> are restricted to those models which are also models of (G, R') where R' is identical to the RIF document R,
> >>> with the addition that R' has additional imports clauses
> >>>
> >>>   Imports( R1 )
> >>>   Imports( G P )
> >>>
> >>> Together with the conditions in section 5.2 this ensures that RIF-X-combinations where R is empty, i.e. which
> >>> are only defined by a set of RDF graphs, can also import RIF rulesets.
> >>>
> >>> ====================================================================================
> >>>
> >>> I think this should work apart from that there is one small issue which I consider possibly "suboptimal"
> >>> as opposed to "owl:imports".
> >>>
> >>> The triple
> >>>    R1 rif:usedWithProfile P .
> >>> is in such case still be considered part of the "data" whereas owl:imports triples are in fact not considered in the OWL direct semantics, right?
> >>>
> >>> maybe those better filled in about "owl:imports" can help, I could actually also try to solicit help/alternative suggestions from people that
> >>> have a more complete understanding on that matter.
> >>>
> >>> best,
> >>> Axel
> >>
> >> --
> >> Jos de Bruijn
> >>   Web:   http://www.debruijn.net/
> >>   Phone: +39 0471 016224
> >>   Fax:   +39 0471 016009
> >>
> >
> 
> --
> Jos de Bruijn
>   Web:   http://www.debruijn.net/
>   Phone: +39 0471 016224
>   Fax:   +39 0471 016009
>

Received on Tuesday, 23 February 2010 10:39:20 UTC