Re: viewpoints and multiple inheritance.
I apologize for sending a hasty message a few minutes before leaving
for vacation. For the simpler folk who are just reading up to the
point where I disagree with them: I ADVOCATE MULTIPLE INHERITANCE.
I hastily said:
>It is because of this almost universal lack of discipline
>that we should consider not having multiple inheritance.
Bill Andersen replied:
> (x):Equiangular(x) -> Polygon(x)
> (x):Equilateral(x) -> Polygon(x)
> (x):RegularPolygon(x) -> Equiangular(x) and Equilateral(x)
> All these are "necessary" definitions, assuming the conventional
>definitions of these terms. This ought to be an example of the
>legitimate use of "multiple inheritance".
> My point is if you can think of one principled example, you can
>probably come up with others. It would be unfortunate if we were
>to "throw out the baby with the bathwater" by failing to allow
>this. All we need to do is to apply a framework, such as the one
>you and Nicola have developed to weed out the silly cases (the C++
>example comes to mind)
Right. Despite my actual words, I do not propose that we completely
abandon multiple inheritance just because most people don't know how
to use it.
Most of the email-avalanche following Nicola's first message were
advocating the ultimate need, in general, for multiple inheritance in
an ontology. THIS I GRANT (in my power to do so), even though most
of the examples were actually bad (or silly) ones.
HOWEVER, "designing a top-level ontology" is much different from
"designing an ontology" in general for some concrete and
domain-specific purpose. While it should be clear that for the
latter, MI is often needed, for the former I believe it is not. In
other words, and I may seem to be changing directions here, I'm not
completely sure multiple inheritance should be allowed in our TOP
LEVEL ontology. At the very least, I believe it should be avoided.
The top level should attempt to carve up the world into discrete
categories as much as possible.
Can we avoid MI completely in the top-level? Perhaps not completely,
but we should try.
Does this mean top-level categories should be disjoint? No.
Disjointness is a different notion. Even if we manage to have a
top-level without MI the top level categories may be overlapping.
Can domain-specific extensions specialize multiple top-level
categories? Yes, the top level categories are not disjoint.
Christopher A. Welty Professore Visitatore
Corso Stati Uniti, 4 Voice: +39 049 8295783
I-35127 Padova Fax: +39 049 8295763