- From: Chris Welty <cawelty@gmail.com>
- Date: Thu, 16 Aug 2007 10:43:37 -0400
- To: Michael Kifer <kifer@cs.sunysb.edu>
- CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
Michael Kifer wrote: >> 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. > > The semantics has been defined formally. But you are right. > foo rif:subclassOf bar should imply foo rdfs:subclassOf bar. > I wrote my reply before having my morning coffee. And better coffee no doubt than I had. > But I do not really see how your proposal is a compromise. It is just a > statement of a fact. Right. That's why I called it a friendly amendment (not a compromise). It doesn't really change anything in your proposal it just makes something explicit. > rif:subclassOf is not a new concept. It is there in > every standard OO language. Jos' arg was that it is a new word in the > vocabulary, and Dave was questioning whether RIF should define such a > concept (incl. rdfs:subclassOf) in the first place. I'm just hoping it makes what you proposed a little more palatable. But let's see - Dave and Jos? Does Michael need still more coffee or do I? -Chris >> 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 >> >> > > > -- 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 14:44:00 UTC