- From: Axel Polleres <axel.polleres@deri.org>
- Date: Thu, 25 Feb 2010 10:02:09 +0000
- To: RIF <public-rif-wg@w3.org>
Hi all, Ivan raised the question why ## was not in RIF Core... I tried to exploit my memories on this as good as I can, but I am not 100% sure whether I got everything right and would seek confirmation of the group. Also, there's a small issue which I don't like and want to raise here... since from the mails below, the thread may be hard to grasp, let me summarise: Ivan asked for the reason of the absence of ## in RIF Core - in the context of modelling rdfs:subclassOf . I didn't really remember precisely the details why we dropped ## from Core, but pointed Ivan to the difference between ## and rdfs:subclassOf , that is, ## not being reflexive. However, what then still worried me a bit is following: Note that http://www.w3.org/TR/rif-rdf-owl/ restricts RDF-OWL interpretations in such a way that ## implies rdfs:subclass but not the other way around. The Embedding of RIF combinations in Section 9.1.3 of http://www.w3.org/TR/rif-rdf-owl/ enforces this by a rule... which then makes even the embedding of simple RDF entailment go outside RIF Core... I am not sure whether I like this. :-| Ivan, suspected even a "bug" here, by the assumption that if I talk about simple and RDF interpretations, I shouldn't worry about the RDFS vocabulary, but I wouldn't go that far: As far as I can see, this is not problematic. We just restrict that when you throw RIF and RDF stuff together, a link is made from ## to rdf:subclasss... that implies that anything which is stated as ## in RIF is exported to rdfs:subclassOf (but NOT the other way around!) only in RIF-RDFS-entailment this would have cross-effects (since RDFS interpretations imply reflexivity on rdfs:subclass), but not in RIF-Simple and RIF-RDF. Still, and here I think Ivan's concern plays a role, I don't like that now for embedding simple RDF or RDF in RIF, I need non-core rules... in fact, it seems to me that the rule in Section 9.1.3 of http://www.w3.org/TR/rif-rdf-owl/ Forall ?x ?y (?x[rdfs:subClassOf -> ?y] :- ?x ## ?y]) )) is irrelevant for Simple and RDF entailments. Particularly, this is the case as long as the RIF ruleset in the combination does not use ##. Can you confirm this? If I had a wishlist, I would opt for moving the semantic condition on "7. IEXT(IS(rdfs:subClassOf)) is a superset of the set of all pairs (a, b) in Dind x Dind such that Itruth(Isub(a,b))=t;" to just apply for RIF-RDFS-models "upwards" Can we still change this? Axel Begin forwarded message: > From: "Ivan Herman" <ivan@w3.org> > Date: 25 February 2010 09:46:04 GMT > To: "Polleres, Axel" <axel.polleres@deri.org> > Cc: "Sandro Hawke" <sandro@w3.org> > Subject: Re: A technical RIF question > > > > On 2010-2-25 10:10 , Axel Polleres wrote: >> >> On 25 Feb 2010, at 09:03, Ivan Herman wrote: >> >>> >>> On Feb 25, 2010, at 09:56 , Axel Polleres wrote: >>> >>>> Phew, IIRC this has some historic reasons, which I don't really remember. >>>> >>>> Firstly, ## is not the same as rdfs:subclass (e.g. ## is NOT reflexive, IIRC) >>>> >>>> The simple solution is, similar to what I answered to Dan on owl:sameAs: >>>> >>>> just use rdfs:subclass in your rules and don't bother about ## they are not the same thing... >>>> >>> >>> Well, o.k. I will try to avoid referring to ## in my tutorial part then...:-( >>> >>>> What worries me a bit more: >>>> Note that http://www.w3.org/TR/rif-rdf-owl/ restricts RDF-OWL interpretations >>>> in such a way that ## implies rdfs:subclass but not the other way around. >>>> The Embedding of RIF combinations in Section 9.1.3 of >>>> http://www.w3.org/TR/rif-rdf-owl/ enforces this by a rule... which then makes even the >>>> embedding of simple RDF entailment go outside RIF Core... I am not sure whether I like this. :-| >>>> >>> >>> Oops. But isn't this a bug? If I talk about an RDF interpretation, than the RDFS vocabulary is immaterial. and subClassOf is in the RDFS vocabulary and _not_ in the RDF vocabulary! >> >> As far as I can see, this is not problematic. We just restrict that when you throw RIF and RDF stuff together, >> a link is made from ## to rdf:subclasss... that implies that anything which is stated as ## in RIF is exportet to rdfs:subclassOf (but NOT the other way around!) >> only in RIF-RDFS-entailment this would have cross-effects (since RDFS interpretations imply reflexivity on rdfs:subclass), but not in RIF-Simple and RIF-RDF >> >> If you agree, I should carry this discussion to the RIF group... >> > > Sure > > Ivan > > >> HTH, >> Axel >> >> >>> >>> I think this is a bug that you should report before this goes to PR:-( >>> >>> Ivan >>> >>> >>>> I am not really swapped in on that at the moment, and for more details and clarifications, >>>> I'd prefer to get back to the group... >>>> >>>> Axel >>>> >>>> On 25 Feb 2010, at 08:22, Ivan Herman wrote: >>>> >>>>> (background: I try to update my tutorial slide set...) >>>>> >>>>> Question: what is the background of the fact that '#' is defined for >>>>> Core and '##' is not? >>>>> >>>>> For many RDF users I would think Core (or maybe strongly safe Core) >>>>> would be the natural rule set to use in the sense that would cover most >>>>> of their needs (at least I believe). The fact of having '#' is fine, it >>>>> is the equivalent of rdf:type. But, for RDFS users, so to say, suddenly >>>>> there is this gap of '##'; either they have to keep to Core and use >>>>> explicitly rdfs:subClassOf, or they use '##', thereby getting into BLD... >>>>> >>>>> So: what is the technical reason for this? >>>>> >>>>> Thanks >>>>> >>>>> Ivan >>>>> -- >>>>> >>>>> Ivan Herman, W3C Semantic Web Activity Lead >>>>> Home: http://www.w3.org/People/Ivan/ >>>>> mobile: +31-641044153 >>>>> PGP Key: http://www.ivan-herman.net/pgpkey.html >>>>> FOAF : http://www.ivan-herman.net/foaf.rdf >>>>> vCard : http://www.ivan-herman.net/HermanIvan.vcf >>>>> >>>> >>> >>> >>> ---- >>> Ivan Herman, W3C Semantic Web Activity Lead >>> Home: http://www.w3.org/People/Ivan/ >>> mobile: +31-641044153 >>> PGP Key: http://www.ivan-herman.net/pgpkey.html >>> FOAF: http://www.ivan-herman.net/foaf.rdf >>> >>> >>> >>> >>> >> > > -- > > Ivan Herman, W3C Semantic Web Activity Lead > Home: http://www.w3.org/People/Ivan/ > mobile: +31-641044153 > PGP Key: http://www.ivan-herman.net/pgpkey.html > FOAF : http://www.ivan-herman.net/foaf.rdf > vCard : http://www.ivan-herman.net/HermanIvan.vcf >
Received on Thursday, 25 February 2010 10:02:43 UTC