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Re: [ontac-forum] Future directions for ontologies and terminologies

To: ONTAC-WG General Discussion <ontac-forum@xxxxxxxxxxxxxx>
From: Lucian_Russell/ESI/CSC <Lucian_Russell/ESI/CSC@xxxxxxx>
Date: Fri, 30 Dec 2005 09:54:30 -0500
Message-id: <OF3F930827.93BFA4DF-ON852570E7.0051D08A-852570E7.0051E5C1@xxxxxxx>

Static vs. Dynamic Queries

Hello from a former lurker. My name is Lucian Russell and my specialty is applying the principles of uncertain reasoning to data, all kinds. I have been in the computer science field for several decades.

One of the decisions one needs to make about an upper Ontology is whether it is needed at all.  If the answer is “yes” then the choice is to create a single upper Ontology that categorizes all human knowledge into a small number of categories. This is by definition static. The other alternative is to have a large number of categories which can be combined on the fly; this is by definition dynamic. This decision entails recognizing the form it would take.  

This initial submission will lay out one issue: the need or not for concept lexicalization for the highest level of a static Ontology. As John Sowa cited the philosopher Aristotle’s timeless insight, I will cite the timeless insight of Gloria Estphan who in the 1980s sang the hit “The Words Get in the Way”.

First off, let me recommend to those who know of WordNet but have never read the book to do so, especially Chapter 1 (nouns) and Chapter 3 (verbs); subsequently read Chapter 2 (adjectives and adverbs) and re-read the two surrounding chapters. To those who have read the book, congratulations for being so well organized and prescient. For those not following WordNet it is up to Release 2.1 and is completing a mapping of words in explanations to senses in WordNet. This latter work will be finished up in April. The current release is available for downloading; it is also on-line for any single word.

Prof. Christiane Fellbaum is the current Principal Investigator (PI) on the WordNet project (Prof. George Miller who started WordNet is old enough that I had him as an instructor for a General Education course while an undergraduate, so is no longer working full time).  She makes the following distinction between WordNet and other Ontologies. WordNet is a lexical ontology. That means that it is based on words in the English Language, though some noun phrases are also included (the words are separated by the underscore character). Although this is generally true, even WordNet contains some non-lexicalized nodes, which brings me to the key question:

1. Should a class name in an Ontology, especially an upper level class, be restricted to a word or phrase?

It would seem that there is something to be said on both sides of this issue.

On the “no” side, for example, WordNet shows that in English verbs there are two senses of the verb “move”. One is movement with a translation in space and one is movement without this change in special position (e.g. spinning). The two senses are not lexicalized but are rather distinct senses of a word with a given spelling (homograph).

On the “yes side” if for a static Ontology there is a single word (or a well known noun phrase) that is used for the name of a class then we have a sound basis for looking at sub-classes and the class membership of instances. In this case we say that the concept is lexicalized.  

A further “yes” argument is that if a concept in the Ontology is not lexicalized then we have to create a name for that concept’s class. But to name it is not to claim it: we cannot claim that our work is done just because we have stung two or more words together. Lacking a linguistic history of our new phase we need to either (1) enumerate the subclasses (in set theory an extensional description) or (2) define a set of inclusion rules (in set theory an intensional description).

Of course we could lexicalize the concept by taking a word from another language that does lexicalize the concept, but if the Ontology is meant for English speakers that new word still needs to be explained to them (the same is true for any language whose words are used to name concepts).

In practice the class membership criteria for instances of an Ontology are specified by a set of constraint rules on property values. Using Descriptive Logic one must be able to reason about the assertion “if X is a class and x in an instance of a thing with property values (a1, a2 …..an) then x is a member of the class X “. The answers are “Yes” and “No”. So for an Ontology a non-lexical class name is really a substitute for a mathematical description.

Static Ontologies, therefore, should probably be ones that primarily use lexicalized concepts in classes. That being the case, it would seem that the logical consequence is that for the top Ontological categories one should use WordNet’s “beginning names” unless there was a REALLY good reason not to do so.

Some researchers in Artificial Intelligence claim they have a better top level Ontology, and maybe they are justified. However, WordNet has some 15 years behind it, so the set-descriptions of the any different concepts should be carefully spelled out so that we may judge.

In the end we can choose what we want; we just should be sure of why we made the choices and know the consequences.

If I have repeated well worn arguments, I will take my deserved newbie lumps and be suitable chastened :-)

Lucian Russell, PhD
Lucian Russell, PhD
Sr. Architect - Principal
Federal Consulting Practice
Computer Sciences Corporation
3110 Fairview Park Drive
Falls Church VA, 22042
Ph: (703)-645-5237
Fax: (703)-645-5233

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