Re: [ontolog-forum] Thing and Class

John said:
You can't use extensional terms such as 'set' and 'class', which
change with every instance that rolls off the assembly line.

My words were carefully chosen, I said: "*The names I [Michael Uschold] find
most useful for these things are...*"

I have not encountered the issues you raise. Apparently you would find other
names more useful - you should use those.

It only becomes an issue if we all have to agree on names, but that is
unlikely to happen any time soon.

Michael

On Mon, Sep 8, 2008 at 6:45 PM, John F. Sowa <sowa@bestweb.net> wrote:

> Ron and Michael,
>
> As I've said many times, the following issues are impossible to solve
> if your hierarchy is limited to a tree, but they are trivial if you
> have a partial ordering (multiple inheritance).  Aristotle's syllogisms
> supported multiple inheritance, Leibniz supported multiple inheritance,
> and I cannot understand why anybody would limit their ontology to tree.
>
> RW> In my experience with Maintenance Management Systems, the definition
>  > of "equipment" and "parts" seemed to be very situational and varied
>  > more with the management history than it did between industries.
>
> All of those variations are legitimate concerns, and all of them must
> be supported.
>
> RW> There could be many revision numbers and dependencies involved
>  > depending on the point of view being considered.  Engineering
>  > specification revisions, supplier revisions, maintenance activity
>  > revisions are frequently unrelated.
>
> All of those representations can be handled (and related to one another)
> with a partial ordering (or a lattice, which is a systematic kind of
> partial ordering).  Don't ever think of a ontology as a tree.  Every
> useful ontology *must* support all possible cross classifications.
> That implies multiple inheritance.
>
> RW> I am not sure that there is a generally accepted way to develop
>  > a general policy on how to design an ontology that handles...
>
> There is.  It's called multiple inheritance, a partial ordering, or a
> lattice.  See the web site for Formal Concept Analysis (FCA), which is
> a widely used lattice system with software (open source) for creating
> and maintaining the lattices:
>
>    http://www.upriss.org.uk/fca/fca.html
>    Formal Concept Analysis Homepage
>
> MU> The names I find most useful for these things are (substituting
>  > into the text above)
>  >
>  >  1. THING: the set of all things in the universe of discourse
>  >  2. CLASS: the set of all things that have member individuals
>  >  3. INDIVIDUAL: the set of all things that do NOT have member
>  >     individuals
>  >  4. ORDINARYCLASS: the set of all things whose members do not
>  >  themselves have members...
>
> As we've discussed many times, the terms 'set' and 'class' are
> extensional, but the categories of an ontology are intensional.
> When Boeing designs a new *type* of aircraft, the *set* is empty
> until the first instance is built.  When any design changes are
> made, the result is a new type or subtype.
>
> But even for a fixed design, the set changes with every instance
> that rolls off the assembly line.
>
> You can't use extensional terms such as 'set' and 'class', which
> change with every instance that rolls off the assembly line.
> It's essential to use intensional terms, such as 'category' or
> 'type'.  Since 'type' takes one syllable instead of four, that
> is a good choice.
>
> John
>
>
>
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