Patrick Cassidy
MICRA, Inc.
908-561-3416
cell: 908-565-4053
cassidy@xxxxxxxxx (01)
I agree with John's suggestion about the use of 'class':
[JS] >
> Jonathan, Mike, Pavithra, and Ed,
>
> As I said before, my primary concern was to clarify some confusion
> about the use of the word 'class'. It is sometimes used as a
> synonym for 'set', sometimes for 'type', and sometimes in a way
> that is not clearly one or the other.
>
> But I admit that the word 'class' has long been used in various ways
> in various systems and that trying to get people to stop using their
> favorite terminology is not easy. Therefore, I suggest that the
> following convention be used to define the notion of class in
> whatever system happens to use the word 'class':
>
> 1. If in system X, the identity conditions for a class are
> determined by extension, then a definition of class in X
> should begin with a phrase similar to the following:
>
> "Every class in system X is a set such that...."
>
> 2. If in system X, the identity conditions for a class are
> determined by intension, then a definition of class in X
> should begin with a phrase similar to the following:
>
> "Every class in system X is a type such that...."
>
> This convention would allow people to continue to use the word
> 'class' whenever they feel the urge to do so, but it would clearly
> specify whether a class is considered as a set or as a type.
>
[[PC]] In the Ontology and Taxonomy Coordinating Working Group (ONTACWG),
we had a vigorous discussion about this terminology topic, and finally put
it to a vote. The result was that a majority of participants chose to use
the term "type" to refer to intensionally specified identity conditions, and
I have used 'type' since then unless I am talking about OWL structures, in
which case I tend to use 'OWL class'. To avoid confusion, I otherwise avoid
the use of the term 'class' except when I am concerned that 'type' may not
be clear to the entire audience, in which case I sometimes use 'type
(class)'. I have not had any use for sets in my ontology work. Since the
instances of any given type depend on the context (time, theory, possible
world, fictional, hypothetical, counterfactual, etc), the type itself can be
identical in all those contexts while the set of instances varies wildly. A
4-D advocate like Matthew West will note that the 4-D view eliminates the
time element from the context set, but that still does not eliminate all the
other ways that a context can be defined, and the problem of multiple sets
for the same type remains. (02)
Pat (03)
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