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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