- From: Chris Welty <cawelty@gmail.com>
- Date: Thu, 16 Aug 2007 08:54:03 -0400
- To: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
Michael Kifer wrote: > Actually, semantically rdfs:subClassOf is a subrelation of rif:subClassOf. > Not the other way around. </chair> I went back and forth on this. I'm not sure it matters that much, as long as rif:subclass is not reflexive. Since you haven't formally defined the semantics of rif:subclass yet, we could go either way. Intuitively, it seemed to me that every rif:subclass relation is an rdfs:subclass relation, but there may be rdfs:subclass relations that a translator will not want to consider as rif:subclass (e.g. the reflexive cases, the cases where one of the arguments is not a class, the case where one of the arguments is a piece of rdf or rif syntax, etc). I guess it depends on whether you want every rdfs:subclass relation (including the entailed ones) in rdf graphs to entail rif:subclass in RIF rules or whether you want a translator to do it. I could go either way. Note that rif:subclass rdfs:subproperty rdfs:subclass does not make rif:subclass reflexive - it does mean that for every A rif:subclass B we would also have A rdfs:subclass A and B rdfs:subclass B, but that's just what rdfs:subclass means. Shouldn't be a problem for rif:subclass. <chair> > > > --michael > > >> </chair> >> Here is a hopefully friendly amendment to the proposal to add a >> rif:subClassOf relation to BLD: >> >> If we just say that <rif:subClassOf rdfs:subPropertyOf >> rdfs:subClassOf> I think it goes part of the way in addressing the >> chief concern of Jos and Dave (which is, as I understand it, that we >> shouldn't add yet another subclass relation to the semantic web). >> >> This would make it clear that we are not really creating something >> new, just imposing a restriction on something already there - in >> particular all rif:subClassOf relations are also rdfs:subClassOf >> relations, but not the reverse, and we would say that rif:subClassOf >> is not reflexive, only holds between classes, etc. >> >> Less the new name, this is what Jos proposed - to define a suitably >> restricted subset of RDFS that would be usable for RIF. I think the >> new name (rif:subClassOf) helps to make it clear that we do not intend >> the full rdfs semantics, rather than "hiding" that in the semantics. >> >> <chair> >> >> -Chris >> >> Chris Welty wrote: >>> >>> Michael Kifer wrote: >>>> Rumblings on why we need classification terms in RIF >>>> (and why RDF's vocab should not be used) >>>> =================================================== >>>> >>>> Two issues: whether we should define facilities for expressing some data >>>> model stuff and whether we should use rdfs for this. >>>> >>>> Rationale: >>>> If we do not have such constructs then everybody will be inventing >>>> their >>>> own. People will not be able to specify any part of their data >>>> model in RIF >>>> which will reduce the usefulness of RIF as an exchange language. >>>> >>>> Why it is not good to use RDF's facilities to define class hierarchies.: >>>> RDF is a foreign language whose semantics is burdened with >>>> non-standard >>>> things. For instance, subclass is reflexive. >>>> >>>> This is bad because not every language out there uses reflexive >>>> subclasses. >>>> For instance, if we map, say, FLORA-2's subclass relationship to >>>> RDFS's then >>>> in the translation (RIF) the query whether foo is a subclass of foo >>>> will >>>> say "yes" but in FLORA-2 it will say "no". >>> </chair> >>> No, no - translating flora2:subclass into rdfs:subclass would be >>> incorrect, because they have different semantics. For me, this is the >>> stronger point in favor of rif:subclass - since so few systems use the >>> rdfs semantics for subclass, very few systems when translating into RIF >>> would use it in their translations. >>> >>> Same for below. You shouldn't translate ilog:subclass into >>> rdfs:subclass. So, in fact, as far as we know, only rdfs based systems >>> would ever use rdfs:subclass when translating through rif, and everyone >>> else would have to invent their own. >>> <chair> >>> >>>> Let's look at some other examples, like ILOG. From my limited >>>> experience >>>> with it, I remember that it uses Java as its data model. So, suppose >>>> there is a class foo in ILOG, which comes from Java. An ILOG set of >>>> rules must not derive "foo sub foo" because this is not true in the >>>> data >>>> model. However, it we translate Java subclass relationship into >>>> rdfs:subclassOf then the resulting RIF translation should generate >>>> "foo >>>> sub foo". (In truth, as I recall, ILOG does not have "sub" in the >>>> heads >>>> of the rules, but it is easy to imagine that next year ILOG is >>>> extended >>>> with something like a query facility. Then their stock will plummet >>>> because their rule sets will not be faithfully exchangeable through >>>> RIF >>>> :-) >>> >>> >> -- >> 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 >> >> > > > -- 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
Received on Thursday, 16 August 2007 12:54:19 UTC