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Re: [ontolog-forum] Thing and Class

To: "[ontolog-forum] " <ontolog-forum@xxxxxxxxxxxxxxxx>
From: "Christopher Spottiswoode" <cms@xxxxxxxxxxxxx>
Date: Thu, 28 Aug 2008 15:52:28 +0200
Message-id: <009a01c90915$54747010$0100a8c0@Dev>
John, thank you, that's just right!    (01)

Christopher    (02)

----- Original Message ----- 
From: "John F. Sowa" <sowa@xxxxxxxxxxx>
To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
Sent: Thursday, August 28, 2008 3:34 PM
Subject: Re: [ontolog-forum] Thing and Class    (03)


> 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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