W3C home > Mailing lists > Public > public-rif-wg@w3.org > December 2007

Re: Another try at subclass

From: Axel Polleres <axel.polleres@deri.org>
Date: Thu, 13 Dec 2007 15:24:21 +0100
Message-ID: <47614095.3000903@deri.org>
To: Chris Welty <cawelty@gmail.com>
CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>

Chris Welty wrote:
> </chair>
> Back in August I proposed a "friendly amendment" for the rif:subClassOf 
> relation (aka ##) saying that:
> rif:subClassOf rdfs:subproperty rdfs:subClassOf .

that would mean that each rif:subClassOf should be a rdf:subClassOf...
aehm... shouldn't it be - if any - just the other way around?

rdfs:subClassOf is more specific.


> 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. Axel Polleres
email: axel@polleres.net  url: http://www.polleres.net/

rdf:Resource owl:differentFrom xsd:anyURI .
Received on Thursday, 13 December 2007 14:31:10 UTC

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