ontology

1. philosophy A systematic account of Existence.

2. artificial intelligence (From philosophy) An explicit

formal specification of how to represent the objects, concepts

and other entities that are assumed to exist in some area of

interest and the relationships that hold among them.

For AI systems, what "exists" is that which can be

represented. When the knowledge about a domain is

represented in a declarative language, the set of objects

that can be represented is called the universe of discourse.

We can describe the ontology of a program by defining a set of

representational terms. Definitions associate the names of

entities in the universe of discourse (e.g. classes,

relations, functions or other objects) with human-readable

text describing what the names mean, and formal axioms that

constrain the interpretation and well-formed use of these

terms. Formally, an ontology is the statement of a logicaltheory.

A set of agents that share the same ontology will be able to

communicate about a domain of discourse without necessarily

operating on a globally shared theory. We say that an agent

commits to an ontology if its observable actions are

consistent with the definitions in the ontology. The idea of

ontological commitment is based on the Knowledge-Level

perspective.

3. information science The hierarchical structuring of

knowledge about things by subcategorising them according to

their essential (or at least relevant and/or cognitive)

qualities. See subject index. This is an extension of the

previous senses of "ontology" (above) which has become common

in discussions about the difficulty of maintaining subjectindices.

(1997-04-09)