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Re: Some thoughts on the semantics of domain and range

From: Graham Klyne <GK@Dial.pipex.com>
Date: Thu, 14 Sep 2000 08:51:54 +0100
Message-Id: <4.3.2.7.2.20000914084036.00b1cf00@pop.dial.pipex.com>
To: guha@guha.com
Cc: www-rdf-interest@w3.org
 > At 10:56 AM 09/13/2000 -0700, guha wrote:
 > >rdfs:domain and rdfs:range were modelled after the similarly named
 > >concepts
 > >in Cycl and have had very well defined meanings right from the beginning.
 > >
 > >(rdfs:domain ?arc ?domain) ^ (?arc ?source ?target) => (rdf:type ?source
 > >?domain)
 > >and
 > >(rdfs:range ?arc ?range) ^ (?arc ?source ?target) => (rdf:type ?target
 > >?range)
 > >
 > >and thats it.

In which case, I think there's a drafting problem in the document, as 
already noted.

--

Responding to the following discussion on conjunctive vs disjunctive semantics.

I think there is a natural tension here between inference and 
expression:  conjunction favours the former, and disjunction favours the 
latter.

My own view (based on limited experience in this area) is that the core 
specification should focus on conjunction, for the reasons already stated 
by others.  I think the expressive power of disjunction (and the 
non-monoticity that incurs) should come through layered descriptions based 
on the RDF core.

For example, I can see possibilities for addressing the issues that Natalya 
raises (in the "wearable" example) using contexts ... but that's another 
debate.

#g
--

At 06:09 PM 9/13/00 -0700, Guha wrote:
[...]
>On the net, disjunctive semantics for range/domain can be a real
>problem. Lets assume that we know that the domain for an arc foo
>is the Class Bar and that a resource baz has the arc foo. With
>disjunctive semantics, the domain information is pretty much
>useless to us since it does not allow us to conclude anything. After
>all, somewhere out there on the web could be another domain
>statement for foo. We could make a CWA and conclude that
>baz is an instance of Bar and if we ever find another domain
>statement for foo, retract our original conclusion.
>
>The place where the single domain/range requirement hurts is
>when the range or domain of an arc tends to be "oddly shaped",
>i.e., not have a single class corresponding to it, but is a conjunct
>or disjunct of mulitple classes where the conjunct/disjunct does
>not define a "natural kind" (as in Quine's use of the term "natural
>kind"). Non-natural kinds are a problem all around.
>
>Allowing multiple domains/ranges with conjunctive semantics solves
>some of these problems without introducing mentioned earlier, but
>we are still left with the other problem mentioned earlier.
>
>We could make a CWA and conclude that
>baz is an instance of Bar and if we ever find another domain
>statement for foo, retract our original conclusion. But the whole
>non-monotonic reasoning using a TMS for dependency maintanence
>game needs to be revisited in the context of inferencing on the web.
>That game was defined based on a KB update model that does
>not neccesarily apply here.
>
>guha
>
>Natalya Fridman Noy wrote:
>
> > At 10:56 AM 09/13/2000 -0700, guha wrote:
> > >rdfs:domain and rdfs:range were modelled after the similarly named
> > >concepts
> > >in Cycl and have had very well defined meanings right from the beginning.
> > >
> > >(rdfs:domain ?arc ?domain) ^ (?arc ?source ?target) => (rdf:type ?source
> > >?domain)
> > >and
> > >(rdfs:range ?arc ?range) ^ (?arc ?source ?target) => (rdf:type ?target
> > >?range)
> > >
> > >and thats it.
> >
> > Actually, Cyc's conjunctive semantics  for domains and ranges can (and
> > does) force modeling choices that sometimes make the whole concept of
> > domain and range practically useless. Here is an example (if memory serves,
> > it comes directly from Cyc). Consider the domain of a property
> > wearingSomething. A natural domain would be Person. However, dogs can also
> > wear something, so we have to make Animal a domain of wearingSomething (by
> > the by, allowing lions to wear things as well). In addition, manikins can
> > wear something. Now we have to go up to TangibleThing making the
> > declaration of domain essentially useless. Similar argument holds for 
> range.
> >
> > This conjunctive semantics for domains and ranges in Cyc was in fact a
> > problem for the OKBC systems when Cyc knowledge bases were translated into
> > frame-based OKBC-compatible KR systems such as Ontolingua and Protege:
> > Since domains and ranges of properties had to be maximally general,
> > high-level classes had hundreds of slots (properties) that had little
> > meaning for that class.
> >
> > In fact, OKBC adopted the disjunctive semantics for domains and ranges of
> > slots (perhaps, for practical reasons), and it seemed to work well there.
> >
> > Natasha

------------
Graham Klyne
(GK@ACM.ORG)
Received on Thursday, 14 September 2000 04:49:03 GMT

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