- From: Jos de Bruijn <jos.debruijn@gmail.com>
- Date: Thu, 01 Apr 2010 10:04:59 +0200
- To: Axel Polleres <axel.polleres@deri.org>
- CC: Chris Welty <cawelty@gmail.com>, RIF <public-rif-wg@w3.org>, Ivan Herman <ivan@w3.org>, Birte Glimm <birte.glimm@comlab.ox.ac.uk>, Chimezie Ogbuji <ogbujic@ccf.org>, Sandro Hawke <sandro@w3.org>
On 2010-03-18 17:35, Axel Polleres wrote: > > On 18 Mar 2010, at 16:01, Jos de Bruijn wrote: > >> I see what you mean. An implementation that does not take one of the >> imports into account does not follow the spec. > > Actually, the other way around: > An implementation that takes rif:imports (that is the imports directive > in the RDF Graph G) into account in the way I proposed, does - strictly > speaking - not follow the SWC spec. > > However, I hope we can get around this, if we define in SPARQL just > what the "corresponding RIF-RDF-combination" to a graph mentioning > rif:imports is. > >> Now, concerning the rif:imports. Could you explain me again why it is a >> good idea to extend the RDF semantics to include RIF-RDF combinations? > > We want a handle from RDF to RIF, just as "Imports()" gives you a handle > from RIF to RDF. We don't want to extend the RDF semantics, but the semantics > of RIF-RDF combinations. It is in fact an extension of the RDF semantics. If you use plain simple entailment you have fewer entailments than when you use RIF-Simple entailment. > >> I understand that you want to use SPARQL to query RIF-RDF combinations. >> How does the syntactic construct in RDF help? > > From SPARQL we can only query RDF Graphs, or, more precisely RDF Datasets. > Entailment regimes, can only extend Basic GHraph pattern matching in SPARQL, > i.e. what a graph means. [1]: > That is, an entailment regime can define the scoping graph for an > RDF Graph G under RDFS Entailment to be a particulalar > canonically defined RDFS entailed graph G'. Similar for OWL. > > So, in a RIF-Entailment regime, we need to say what the Graph "means" wrt. RIF, > but there we need a handle to RIF, such that we can define that scoping graph > as a graph entailed by the RIF-RDF-combination defined by rif:imports triples. > We have no means to refer directly to a RIF ruleset from SPARQL, but only to > RDF Datasets. I see what you mean. Why not add the possibility to refer to something else than an RDF dataset? This seems cleaner than defining a same-syntax semantic extension of RDF. As you may have gathered, I don't like such extensions ;) > >> Why not have implicit >> rulesets (like the implicit datasets) and give the user the possibility >> to refer to a RIF ruleset from the query? > > You also don't want to fix the ontology for OWL Entailment, but anyways > OWL fits a bit better with the RDF dataset idea, since you can express OWL > in RDF, or import OWL ontologies, so we are safe there. > > Extending the definition of Dataset towards something else then RDF Graphs > is outside the scope of entailment extensions in SPARQL. It might make sense to bring it in scope. Anyway, that's just my opinion. Cheers, Jos > > Hope that clarifies matters, > Axel > > 1. http://www.w3.org/TR/rdf-sparql-query/#sparqlBGPExtend > >> Jos >> >> On 2010-03-18 11:18, Axel Polleres wrote: >>>> I'm not sure what you mean with the imports mechanism having a >>>> semantics. The semantics of the combination (R2,G) is clearly defined in >>>> the SWC spec. >>> >>> Yes it is clearly defined, and it wouldn't take the import of R1 from G >>> into account. So, in case we define a semantics for importing rulesets >>> from graphs, an implementation that takes this imports-mechanism into >>> account will not be compatible to the SWC spec on this example. >>> >>> Axel >>> >>> On 18 Mar 2010, at 10:10, Jos de Bruijn wrote: >>> >>>> >>>> >>>> On 2010-03-12 15:32, Axel Polleres wrote: >>>>> On 12 Mar 2010, at 14:09, Chris Welty wrote: >>>>>> Axel, >>>>>> >>>>>> I really really really do not understand why it matters whether RIF specifies this or SPARQL. >>>>>> RIF should be viewed as read-only right now unless there is an error. >>>>> >>>>> 1) the *main issue* is the URI we use for dereferencing, which we think should be in the rif: namespace, i.e. we need >>>>> rif:'s blessing if we do so. >>>>> >>>>> >>>>> I mentioned in the mail already that it would probably be an alternative if we could just produce a (joint?) >>>>> note or separate (rec?) document on this. That would mean we wouldn't touch the rif-rdf-owl spec as such. However ... >>>>> >>>>> 2) ... as I see it there is *potential issue* around a separate spec which worries me a lot... >>>>> if we *don't* specify the importing from RDF within rif-rdf-owl, then whatever we write in that note separate spec >>>>> would be potentially incompatible with rif-rdf-owl ... here's why: >>>>> >>>>> Say you have two rulesets R1, R2 and one graph G: >>>>> >>>>> G: >>>>> G <> rif:imports [rif:ruleset R1 rif:profile <...simple...> ]. >>>>> >>>>> R2: >>>>> Imports( G <...simple...> ) >>>>> ... some rules ... >>>>> >>>>> R1: >>>>> (Imports R2) >>>>> ... some other rules ... no imports clause >>>>> >>>>> Now... depending on whether or not the imports-mechanism in RDF has a semantics, the RIF-RDF combination (R2,G) >>>>> has different semantics. >>>> >>>> I'm not sure what you mean with the imports mechanism having a >>>> semantics. The semantics of the combination (R2,G) is clearly defined in >>>> the SWC spec. >>>> >>>> >>>> Cheers, Jos >>>> >>>>> >>>>> So, my worry is, if we postpone that issue to post-RIF, we can't define it in an upwards compatible way at all... >>>>> besides, I think it is a very minor change, which makes live much easier for applications coming from the RDF side >>>>> doing something with RIF and doesn't seem to affect 99% of those caring from the RIF side only. >>>>> >>>>> Axel >>>>> >>>>> >>>>>> -Chris >>>>>> >>>>>> Axel Polleres wrote: >>>>>>> Hi all, >>>>>>> >>>>>>> We had the topic of "rif:imports" coming up in SPARQL again in our Entailment regimes taskforce call this week. >>>>>>> >>>>>>> The reason why we (from the SPARQL side) would prefer to have that imports mechanism defined in RIF, >>>>>>> is mainly that we think that the URIs to use for defining this imports mechanism should be in the rif: >>>>>>> namespace, since this imports mechanism is likely useful not only for SPARQL but also for other >>>>>>> RDF applications that wnat to interact with RIF. >>>>>>> >>>>>>> Thus, I wanted to inquire again, whether we'd have a chance to get that an import mechanism for RIF from RDF into >>>>>>> http://www.w3.org/TR/rif-rdf-owl/ ? >>>>>>> >>>>>>> If the group overall still thinks that it is too late to get this into the spec, in turn, I wanted to ask/raise >>>>>>> again how/whether we could proceed to publish this text as a WG Note? >>>>>>> >>>>>>> I have earlier made a simple proposal to add a new section to the current spec, which we elaborated a bit now: >>>>>>> >>>>>>> 1) In the introduction of http://www.w3.org/2005/rules/wiki/SWC, >>>>>>> I would suggest to add: >>>>>>> >>>>>>> "RDF Graphs in RIF-RDF-combinations are assumed to not contain any triples using the predicates >>>>>>> rif:imports, rif:ruleset and rif:profile we refer to Section 6 for treatment of such graphs. >>>>>>> " >>>>>>> >>>>>>> 2) Further, I would suggest to add a new section: >>>>>>> ==================================================================================== >>>>>>> >>>>>>> = 6 Importing RIF rulesets in RDF = >>>>>>> >>>>>>> The definitions so far, only covered RIF-RDF-combinations where the RDF graphs did not contain >>>>>>> triples using rif:usingRuleset in predicate positions. To lift this restriction, we define >>>>>>> RIF-X-combinations (R,S) where any of the graphs in S contains triples with the predicates >>>>>>> rif:imports, rif:ruleset and rif:profile >>>>>>> by a reduction to combbinations without such triples as follows. >>>>>>> >>>>>>> Let (R, S) be a combination as above. The reduction of R is defined as the >>>>>>> RIF-X-combinations (R', S') where >>>>>>> (i) S' is identical to S with all rif:imports, rif:ruleset and rif:profile triples removed, >>>>>>> and >>>>>>> (ii) R' is identical to the RIF document R, >>>>>>> with the addition that R' has additional imports clauses >>>>>>> Imports( R1 ) >>>>>>> Imports( G P ) >>>>>>> for any triples >>>>>>> >>>>>>> <> rif:imports [rif:ruleset R rif:profile P ]. >>>>>>> >>>>>>> in (simple entailed by) S, such that 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 >>>>>>> >>>>>>> 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. >>>>>>> >>>>>>> ==================================================================================== >>>>>>> >>>>>>> In case there is a chance to get this on one of the next agendas, please let me know, since I have recently not >>>>>>> really had time to be follow the RIF TCs, but I'd be joining for that. >>>>>>> >>>>>>> best, >>>>>>> Axel >>>>>>> >>>>>>> P.S.: Condition (i) which removes all the rif:usingruleSet triples, i.e., >>>>>>> just treats these triples as a directive rather than part of the graph, may be dropped, i.e. simply >>>>>>> keeping S as is, accepting the rif:imports, rif:ruleset and rif:profile triples as part of the graph. >>>>>>> >>>>>> >>>>>> -- >>>>>> Dr. Christopher A. Welty IBM Watson Research Center >>>>>> +1.914.784.7055 19 Skyline Dr. >>>>>> cawelty@gmail.com Hawthorne, NY 10532 >>>>>> http://www.research.ibm.com/people/w/welty >>>>>> >>>>> >>>>> >>>> >>>> -- >>>> Jos de Bruijn >>>> Web: http://www.debruijn.net/ >>>> LinkedIn: http://it.linkedin.com/in/josdebruijn >>>> Skype: josdebruijn >>>> Google Talk: jos.debruijn@gmail.com >>>> Mobile phone: +43 660 313 5733 >>>> >>> >> >> -- >> Jos de Bruijn >> Web: http://www.debruijn.net/ >> LinkedIn: http://it.linkedin.com/in/josdebruijn >> Skype: josdebruijn >> Google Talk: jos.debruijn@gmail.com >> Mobile phone: +43 660 313 5733 >> > -- Jos de Bruijn Web: http://www.debruijn.net/ LinkedIn: http://it.linkedin.com/in/josdebruijn Skype: josdebruijn Google Talk: jos.debruijn@gmail.com Mobile phone: +43 660 313 5733
Received on Thursday, 1 April 2010 08:05:31 UTC