John: (01)
I have been toying with these problems ever since I got introduced into the
ontologists world. One thing that bothers me with a lot of ontology work is
the lack of a context modifier concept. Context is such an important
aspects of cognitive behavior and semantics in general. A tree is not
always a tree, a river is not always a river. A glass of water sitting on a
desk in front of you will not be elevated in your own tuple stores yet a
glass of water approaching your windshield at 60MPH will based on your
perception that it is a threat to your safety. They are the same object but
in different contexts have different meaning. (02)
Even the basic examples that used to come with Protégé were flawed IMO. The
wine example was screaming for the aspect of context to be included in the
ontology given the concept of "best wine" is contextually dependent upon
your definition and criteria for "best". Does it mean that I think it is
the best? Is the the author of the ontology? Has some universally accepted
criteria been applied and used to judge it? Without the definition of
"best", the example is largely confusing and meaningless IMO. (03)
There have been some work done around context. Most of it has failed or
resulted in an open ended explosion of hypothesis. (04)
It is my hope that one day a serious effort will start to really open this
topic up. (05)
Duane (06)
On 2/14/07 9:41 AM, "John F. Sowa" <sowa@xxxxxxxxxxx> wrote: (07)
> Pat, Chris, Kathy, and Barry,
>
> The problem of stating necessary and sufficient conditions
> for defining anything is nontrivial, even in mathematics.
> For phenomena in nature or the results of typical human
> behavior, definitive statements are problematical, to say
> the least.
>
> Belief revision systems, database systems, and knowledge-based
> systems distinguish levels of "entrenchment" (whether or not
> they use that term), and I believe that an ontology should also
> make such distinctions at the metalevel. Following are some
> "levels of entrenchment" in descending order of strength:
>
> 1. Type hierarchy. The classical tree or partial ordering
> introduced by Aristotle and first drawn by (or attributed
> to) Porphyry. It's useful in every field, it's not going
> away, and we should recognize it as the minimal requirement
> for an ontology.
>
> 2. Necessary distinctions. The differentiae that split any
> type into two or more subtypes. If the split is binary
> (A or not-A), then it is both necessary and sufficient for
> distinguishing the two subtypes from one another, but the
> conditions for characterizing the supertype might not be
> necessary and sufficient.
>
> 3. Constraints. Additional statements that characterize the
> types or the interactions of entities of various types.
> The constraints are necessary relative to the ordinary
> facts in level #4, but they might not be considered
> defining characteristics.
>
> 4. Ordinary facts. Ground-level assertions that must be
> consistent with statements at the above levels, but they
> may violate defaults at level 5.
>
> 5. Defaults and probabilities. Statements that are usually
> true of entities of a given type or types, but they are
> at the bottom of the entrenchment pole. A probable
> statement is a default with an associated value that
> indicates its likelihood or frequency of occurrence,
> given the occurrence of some other condition.
>
> Systems of entrenchment levels along such lines are widely
> used and should be supported. Cyc, for example, has 3 levels:
> True, true by default, unknown (and the negations -- false
> by default and false). But I think that Lenat would agree
> that a privileged level should be added for some of the
> axioms, especially ones that define the type hierarchy.
>
> A declaration of which level a particular statement belongs to
> would not be part of the first-order theory, but it would be
> a metalevel statement that should definitely be considered
> part of the ontology.
>
> John
>
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