What is color? What is red? (01)
Cory Casanave wrote: (02)
>Ok, logical gurus, help me out here.
>The asserted "difference", between type and class is extensional. The
>statements below say that if the instances satisfying the types are the same
>then types are the same.
>Another statement would be if the instances satisfying the types must be the
>same the types must be the same.
>The <are> and <must be> are very important.
>
>The first statement would only work for predicates that assume a very closed
>and very static world. E.G. the type of people on this list and the type of
>people with 874 hairs on their left arm are the same so these types must be
>the same - a very bad inference, particularly after I pluck a hair. It
>assumes global knowledge and a static world. While I have no problem that
>predicates or even logics may choose to make those assumptions, it should
>not be part of the definition of type (or class).
>If, on the other hand there is a logical necessity for the extensions to be
>the same, the class and type concepts are the same - this works and I don't
>see the issue. This also works in OWL. This is what I thought the concept
>of extensional classes entailed - but I am still learning.
>As Chris says, you can ADD those assumptions to an ontology or context
>without constraining core concepts like type/class/isKindOf.
>
>
>-----Original Message-----
>From: ontac-dev-bounces@xxxxxxxxxxxxxx
>[mailto:ontac-dev-bounces@xxxxxxxxxxxxxx] On Behalf Of Chris Menzel
>Sent: Friday, January 20, 2006 12:33 PM
>To: ONTAC Taxonomy-Ontology Development Discussion
>Subject: Re: [ontac-dev] Type vs. Class -- Please vote
>
>On Fri, Jan 20, 2006 at 06:27:49PM +0200, Christopher Spottiswoode wrote:
>
>
>>...
>>
>>
>
>Hello, Christopher, it's been a while.
>
>
>
>>Pat, my own vote goes strongly to "type" (if I may emerge albeit
>>perhaps incongruously from my lurking state on this list).
>>Im my own work, which I hope to release to this list and the widest
>>user community at a more appropriate time, I have for many years
>>consistently and insistently used "type" to denote the intensional
>>sense. "Class", it seems to me (as to John Sowa), invites confusion
>>with the extensional sense.
>>
>>
>
>I continue to be utterly flummoxed by this argument. Do we, or do we
>not, believe ontologies can avert exactly these sorts of confusions?
>If not, just what do we think we are doing? Looky here:
>
>(forall (C1 C2)
> (if (and (Class C1)
> (Class C2)
> (forall (x)
> (iff (instanceOf x C1)
> (instanceOf x C2))))
> (= C1 C2)))
>
>Add that axiom to your ontology, you get extensional classes. Leave it
>out, you don't. Simple, eh? :-) What *is* the controversy here?
>
>
>
>>Having said that, I would however agree with Cory that we should try
>>to conform as far as possible with what seems like colloquial use.
>>But I think that that rather argues in favour of "type", as it is (to
>>me at least...) more colloquially intensional than "class"!
>>
>>
>
>Well, at the risk of furthering the impression that this red herring of
>an argument is to the point :-) , I respectfully disagree. Indeed, I
>can't even think of a colloquial use of the term "class" that is
>extensional. Not even "set" is extensional in colloquial usage.
>
>
>
>>I mention that because both Chris Menzel and Leo Obrst have warned us
>>against using "type" because of all the uses of that word in various
>>formal systems.
>>
>>
>
>That skews my point badly. It is not simply the fact that "class" is
>the term of choice in the formal system OWL that we should use it; it is
>the fact that it is in OWL AND the fact that OWL and its kin are the
>primary W3C languages for publishing ontologies on the web. We're
>swimming unnecessarily, indeed perversely, upstream if we choose
>otherwise. Seems to me that the only thing that could justify the
>choice of "type" would some definite semantic incompatibility between
>the desired ONTAC notion and the W3C notion of class. But there isn't.
>So if we go with "type", we force EVERY user of OWL out there who wants
>to interact with an ONTAC-based ontology needlessly to worry about
>translating every occurrence of "type" into "class". Similarly for
>every user of any ONTAC-based ontology. Isn't the point here to
>*enhance* interoperability? Why throw up this completely unnecessary
>stumblingblock, folks?
>
>
>
>>I would strongly urge us, however, not to be so influenced by such
>>perhaps confusing formal uses:
>>
>>
>
>It is the informal uses that are confused. We have axioms to prevent
>that sort of confusion.
>
>-chris
>
>
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> (03)
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