To evaluate an ontology, we need to distinguish the requirements
for the upper-level ontologies, the middle levels, and the low-level
microtheories. Philosophy dominates the upper levels. Very narrow,
very specific problems dominate the lower levels. And terminologies
for various application domains dominate the middle levels. (01)
The criteria for evaluating an ontology are different for each level.
Following is an excerpt from a note I sent to Ontolog Forum in response
to Chris Partridge. (02)
After the excerpt, I added more discussion about the criteria
at different levels. (03)
John (04)
-------- Original Message --------
Subject: Re: [ontolog-forum] Ontologies and individuals
Date: Sat, 22 Dec 2012 10:35:17 -0500
From: John F Sowa (05)
... (06)
CP
> It is true that if one aims for a consistent organisation over a large
> amount of data, one is faced with situations where the local fit can be
> difficult. (07)
Not just difficult, but *impossible* -- and least until all possible
questions of science have been asked and answered. Furthermore, even
if we had a perfect fit globally, we would still need different and
*mutually contradictory* local approximations. (08)
I keep giving examples from physics, which is the hardest of the hard
sciences. We still do not have a consistent global theory, but we do
have some theories that are more general than others. The best we
have today is QCD (quantum chromo-dynamics). (09)
But nobody uses QCD for any practical application. Applied physics is
a hodge-podge of mutually contradictory approximations. As the slogan
goes, "All models are wrong, but some are useful." (010)
CP
> When a top ontology has been introduced, the turnaround has reduced
> significantly. The top ontology gives a framework for focusing
> the discussion. (011)
I strongly agree. But that top level must be very underspecified,
and the specific ontologies for different purposes from different
points of view will inevitably be mutually inconsistent. (012)
Furthermore, there is no such thing as one ideal top level.
A 4D ontology is great for many purposes, and a 3D ontology
is better for others. (013)
For interoperability, you do not need agreement at the top level,
which is only "a framework for focusing the discussion." And you
do not need agreement at the lowest levels, which are extremely
problem specific. (014)
Where you do need agreement is at the middle level of the words
that people use to talk about a subject. That is why I believe
that Schema.org (and the GoodRelations ontology) have hit the
"sweet spot" of specifying a useful, underspecified middle level. (015)
Charles Sanders Peirce stated some fundamental principles, which
I believe are essential for guiding ontology design and use:
> It is easy to speak with precision upon a general theme.
> Only, one must commonly surrender all ambition to be certain.
> It is equally easy to be certain. One has only to be sufficiently vague.
> It is not so difficult to be pretty precise and fairly certain at once
> about a very narrow subject. (016)
In other words, you can do your precise reasoning at the lowest levels
(about very narrow subjects). Your upper level (general themes) can be
precise, but only as one of many possible frameworks or guidelines.
For the middle levels, it's easy to be certain if you keep them
"sufficiently vague." (017)
Many people have been unhappy about Schema.org because of their lack
of axioms. But that's necessary to keep it "sufficiently vague" to
support interoperability among an open-ended variety of systems.
GoodRelations, which has been adopted by Schema.org, is another
example of a good, "sufficiently vague" middle level. (018)
Fundamental criterion for evaluating a middle level: Consistency
with a variety of different upper levels and the ability to support
interoperability among lower levels designed for different purposes. (019)
John (020)
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