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Re: [ontolog-forum] Ontology of Rough Sets

To: ontolog-forum@xxxxxxxxxxxxxxxx
From: "John F. Sowa" <sowa@xxxxxxxxxxx>
Date: Tue, 18 Jan 2011 23:36:02 -0500
Message-id: <4D366A32.8030908@xxxxxxxxxxx>
Tara,    (01)

I sympathize with your concerns.  I have not been happy about the
use of the word 'class' in OWL and other languages, since the common
use of 'class' in English is very set-like.    (02)

> The part of John's definition that I am questioning is the phrase "a
> "a class is a set that ...".    (03)

There are two parts to the definition:  a set of instances, and a
specification that characterizes the instances.    (04)

That would be true of common English examples, such as an Math class.
I have no objection to a technical use that makes the common usage
more precise (narrow), but I don't like technical terms that *exclude*
the common usage.    (05)

> I looked at every occurrence of the word "class" at this link, and
> I don't see anywhere that it says that a class is a set, or not a set,
> or a collection, or a ....   The extension of a class consists of individuals,
> fine ... so the extension is a set, but that doesn't make the class a set.    (06)

The authors of that OWL semantics document were well trained in logic
and set theory.  So they were very careful not to say that a class is
a set.  But then an OWL math-class would not be an English math-class.    (07)

That's why I don't like the OWL choice of terminology.    (08)

In my suggested definition, I hoped to bridge the gap between the
English sense and the OWL sense.  Perhaps the best thing would be
stick to my original intuitions:  OWL classes really are types,
and the designers of the language make a poor choice of terminology.    (09)

John    (010)

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