Pat, (01)
We (and many others) have been debating various issues about
ontology for multiple decades without reaching any kind of
agreement. The voluminous archives of the SUO mailing list
(from around 2000 AD), the SRKB mailing list (1991 AD), and
several others attest to that fact. (02)
If people who have seriously thought about the issues don't
make some recommendations, somebody who hasn't thought about
them will write a tool or language that becomes widely used,
and we are going to be forced to live with it. (03)
> First, we would have to decide what the right set of "levels"
> should be. Should there be 5 of them, as you suggest? Or 3, as
> Cyc has chosen? Four? Twelve? Perhaps the whole idea of a total
> order is wrong: can the levels be *partially* ordered? (There's
> a PhD thesis lurking there.).......... (04)
Not just lurking. In my KR book, I recommended partial orderings
(note plural) based on Benjamin Grosof's dissertation of 1992. (05)
Recommendations: (06)
1. The importance of levels of entrenchment should be recognized. (07)
2. At the very minimum, there should be three levels: (1) the
statements that specify the type hierarchy, (2) other axioms
(called "constraints"), (3) ordinary factual assertions. (08)
3. Other levels should be optional, any number should be permitted,
and they must be partially ordered (with those three as part
of the ordering). (09)
4. As Kathy has emphasized, probabilistic statements are extremely
important for many domains, especially medicine. They can be
accommodated by one or more levels that are below the facts
in entrenchment. (010)
I certainly agree that more applied research would be valuable,
but an enormous amount of research *and* practice has already
been done over the past 30 years. We should recognize it and
make some recommendations for how it should be accommodated. (011)
John (012)
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