[topicmapmail] Getty Art and Architecture Thesaurus On Line

[Murray Altheim]

Lars Marius Garshol wrote:
> * Thomas B. Passin
[...]
> | Rather, this is the class/instance conundrum.  Is an "instance" of a
> | class supposed to be a class or an individual?  If it is supposed to
> | be an individual, you would not say "Homo Sapiens instanceOf
> | Species".  If it is allowed to be a class, how do you know how to
> | distinguish an instance as a class form an instance as an
> | individual?
> 
> I think this is a non-problem introduced by thinking that classness
> and individuality are somehow absolute. (I think this is the same as
> what Murray replied, but I'm not sure.) You need to define what it
> means to be a class and what it means to be an individual. Once you've
> done that the rest is easy.

Yes, this is what I've been saying. But I hardly would agree that it's
an easy thing, either to make those definitions, or to use them
clearly, unambiguously, and without error. It requires very careful
modeling.

> The Omnigator (which has an index of individuals) defines being an
> individual as not being a type for any instance.

This is actually what I've been saying is a mistake, that absent a
context, being a type for any instance would preclude things like
zoological taxons (like "genus" and "species") from being instances
of "zoological taxons". You must keep track of class-instance within
a specific context. Very few things are *universally* classes or instances.

> | This has been discussed before, in this and other lists, but I
> | confess that I am still not clear on how to deal with the issue
> | except to rule that an "instance" by definition means an individual
> | member of some class.  I gather that this is not altogether
> | satisfactory because sometimes one does want the individual to be a
> | class -
> 
> You assume that being an individual (by your definition) and being a
> class is mutually exclusive, but that's not how topic maps work. So
> I'm not sure there is a problem here.

I don't think there is if the context in which a thing is an instance
is made clear in the way one models it in the topic map.

> | although this is getting into the dangerous waters of the class of
> | all classes
> 
> If you are worried about mathematical consistency, yes. Otherwise, no.

I don't think this is in any way mathematically inconsistent. It's
merely a matter of keeping track of context. I think there's an early
paper from McCarthy's situational calculus on this, but I can't find
it right now. There's also Manos Theodorakis' doctoral dissertation on
"Contextualization", which has quite a lot to say on this subject.

Murray

...........................................................................
Murray Altheim                         http://kmi.open.ac.uk/people/murray/
Knowledge Media Institute
The Open University, Milton Keynes, Bucks, MK7 6AA, UK                    .

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