On Jul 26, 2009, at 8:17 PM, Dave McComb wrote:
> We teach a class in OWL. My sense from our students confusion is
> that the main point of departure between what you understand and
> what's occurring in an ontology comes down to the distinction
> between intensional and extensional sets. (01)
Dave, I think the distinction here is better cast as the difference
between intensional and extensional *definitions* of sets.
"Intensional set" seems to me to be an oxymoron, as sets are by
definition extensional, i.e., Set1 = Set2 iff every member of Set1 is
a member of Set2. However, one and the same set can be *defined*
intensionally, i.e., by means of a description (e.g., {x | x is a US
Senator from Texas}) that might in fact pick out *different* sets at
different times, or extensionally, i.e., by simply listing its members
(e.g., {John Cornyn, Kay Bailey Hutchison}). (02)
-chris (03)
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