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Re: [ontolog-forum] Thing and Class

To: "'[ontolog-forum] '" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: "Patrick Cassidy" <pat@xxxxxxxxx>
Date: Thu, 28 Aug 2008 11:07:15 -0400
Message-id: <018701c9091f$c1d22260$45766720$@com>
I agree with John, for the reasons he cited, that 'type' is now preferable
to 'class' and 'entity' preferable to 'thing' as a generic term for
*anything that is to be discussed*.  In the COSMO I use the term 'type' to
refer to OWL classes, but because the current COSMO version is in OWL, I
sometimes use 'type (class)' or 'type (class, sort, kind)' in the comments
where I suspect that in the context the meaning may not be clear to those
familiar only with the OWL terminology.  I hope this doesn't provoke a
discussion of whether type, class, sort and kind are synonymous, since they
are not used in COSMO with that intention.    (01)

Pat    (02)

Patrick Cassidy
cell: 908-565-4053
cassidy@xxxxxxxxx    (03)

> -----Original Message-----
> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-
> bounces@xxxxxxxxxxxxxxxx] On Behalf Of John F. Sowa
> Sent: Thursday, August 28, 2008 9:34 AM
> To: [ontolog-forum]
> Subject: Re: [ontolog-forum] Thing and Class
> Azamat and Antoinette,
> Developing a good meta-level ontology for talking about ontology
> and its relationship to various applications is important, and
> poor choices can lead to endless confusion.  (Even initials can
> lead to confusion when they're ambiguous, e.g. AA in this case.)
> Azamat> The interrelations of classes as well as classes and things
>  > are actually more subtle and deep, than generally presented in
>  > various specifications...
> I certainly agree.
> Antoinette> I consider, that in this common world, people are NOT
>  > things. People place or thing...
> There is a time-honored international terminology for logic and
> ontology that was derived from Greek and Latin.  Some people have
> objected because the terms are often long and unfamiliar.
> One such word is 'entity' from Latin 'entitas', which literally
> means anything that exists.  It does not have any associated
> baggage of familiar associations, and it can be associated with
> cognate terms in many other languages.  If some languages don't
> have a native word for 'entity', they can just borrow 'entitas'.
> The word 'thing', however, has too many familiar associations,
> and the corresponding familiar terms in other languages have
> different associations.  Therefore, it is very hard to translate
> the word 'thing' to rough equivalents in multiple languages
> without creating different confusions in each language.
> The word 'class' is another term that creates multiple confusions
> because it also has multiple and confusingly different meanings
> in mathematics, programming languages, and common English usage:
>   1. In mathematics, the word 'class' is sometimes used as a synonym
>      for set by some authors, and it is sometimes used as a term
>      for a set-like collection that is too big to be a proper set.
>   2. In object-oriented programming languages, the word 'type' was
>      commonly used for data types.  But the OO languages introduced
>      a kind of entity that was different from a traditional datatype
>      because it had associated procedural "methods".
>   3. In common English usage, the word class is used confusingly in
>      ways that are synonyms for 'set' and in ways that are synonyms
>      for 'type'.  For example, one could talk about the class of
>      students in a room or the set of students.  But there are other
>      uses that refer to the type rather than any particular set,
>      as in 'middle class', 'upper class', or 'first class'.
> Some time ago, we had had a discussion on this list about whether
> we should use the term 'type' or 'class' for the categories of an
> ontological hierarchy.  Both Barry Smith and I were strongly urging
> people to use the word 'type' rather than 'class', but many others
> wanted to use 'class' because it was, unfortunately, used in OWL.
> There was a vote, and the word 'type' won.  But there was a lot
> of grumbling by people who were using OWL.
> I believe that the OWL developers made a very serious mistake in
> adopting the term 'class' because of its association with OO languages.
> That should have been a strong argument against using the word 'class'
> because ontological categories are very different from OO classes.
> But the main reason for not using the word 'class' is its association
> with the purely extensional set theory:  a set (or class) is uniquely
> defined by its instances.  A type, however, is an intensional term,
> and two types may be distinct even when they have exactly the same
> instances (or no instances at all).
> For example, the empty set is a subset of every other set.  The set
> of unicorns is empty; therefore, it is a subset of the set of cows.
> But the type Unicorn is very different from the type Cow.  Other
> examples, include the set of all human beings and the set of all
> featherless bipeds.  Today, those sets are the same, but the types
> have very different definitions.
> Many dinosaurs, such as T. Rex, were bipeds.  Some of them had
> feathers, but no one knows whether they all had feathers.  But
> if some of them didn't, it would be a mistake to call them
> human beings.
> So I recommend that we drop the words 'thing' and 'class' when
> talking about ontologies, and use the terms 'entity' and 'type'.
> John Sowa
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