# Re: Which ontologies; how to compare them

phayes@cs.uiuc.edu
```Date: Thu, 17 Mar 1994 22:25:38 -0800
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Subject: Re: Which ontologies; how to compare them
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```At  6:37 AM 2/17/94 -0600, Fritz Lehmann cited Roberto Poli:

......
>Let's call U the space of observators. For any element u of U we associate a
>new space S(u) in which the phenomenon F is represented by the object O(u).
>At this object we can associate new spaces representing its qualities, etc.
>It is obvious that when we move from the observator u to the observator
>u + du the object changes from O(u) to O(u) + dv. We have objective
>phenomena when there are some connections between du and dv (that is
>between the variation of the observator and the variation of the object).

But this is not obvious. This claim amounts to saying that the mapping of u
to O(u) is continuous. But for example, consider the appearance of a
complex object as it is rotated. Notoriously, the outline is a highly
discontinuous function of time even when relative motion is smooth. The
mapping is better described in terms of catastrophe spaces than as
continuous in any ordinary sense; but we perceive the object as objective.

>...... Consider now the
>lenght/breadth opposition. No thing has lenght without having also some
>breadth (and viceversa). We can build up things that have only lenght and
>no breadth, but such things are ideal things, not real ones (if you prefer:
>abstract, not concrete things).

I disagree. The edge of my ruler has length but no breadth, but it is quite
concrete; for example, it has a nick in it. I suspect that Poli means
'physical object' here. But my world is full of concrete things which are
not whole physical objects, such as temperatures, pressures, edges and
surfaces. One who wishes to argue that these are abstract must surely
explain how to distinguish them from such obviously abstract things as
numbers.

Pat Hayes

PS Fritz, thanks for forwarding the fascinating discussion to Interlingua;
however I have not sent this reply there.

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