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Re: Another try at subclass

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Thu, 13 Dec 2007 00:30:43 -0500
To: Chris Welty <cawelty@gmail.com>
Cc: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
Message-ID: <18596.1197523843@cs.sunysb.edu>



These two proposals are orthogonal. The classification stuff is not the
only impasse. My proposal solves 3 of them and opens a general way of
getting rid of others, which we might encounter in the future.


	--michael  

> </chair>
> 
> Back in August I proposed a "friendly amendment" for the rif:subClassOf relation 
> (aka ##) saying that:
> 
> rif:subClassOf rdfs:subproperty rdfs:subClassOf .
> 
> Michael was not opposed, he thought that it was obvious.  Jos replied as below, 
> indicating some possible softness on the point.  I don't think DaveR responded. 
> But I didn't push on it as some other thing must have come up (like vacation 
> probably), and the thread ended with Jos' message below.
> 
> So before we give up on it, because I do think it would be useful to have in 
> BLD, I'd like to see if this will make a difference to anyone, specifically the 
> objectors to having rif:subClassOf (DaveR, Jos, ?).
> 
> -Chris
> 
> <chair>
> 
> Jos de Bruijn wrote:
> > <snip/>
> > 
> >>> 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?
> > 
> > My argument was that there are already semantic Web languages for
> > defining ontologies (including the subclass relation), so that RIF
> > should probably not invent a new vocabulary for defining ontologies (or
> > classifications), but rather show how existing vocabularies for ontology
> > definition (including (subsets of) RDFS) can be combined with the RIF.
> > 
> > Chris' proposal (rif:subclass rdfs:subproperty rdfs:subclass; use
> > rdf:type for instance statements?) seems to extend the RDFS vocabulary,
> > rather than creating a new vocabulary.
> > This could be a possible way to go for exchanging data models which do
> > not have reflexive subclass statements; however, I am not 100% convinced
> > that we need this extension.
> > 
> > I guess an important question is really whether people want to use
> > several different data models in the same RIF rule set.
> > 
> > 
> > Best, Jos
> > 
> > 
> >> -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, 13 December 2007 05:30:52 GMT

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