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 logical theory.
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 subject indices.
(1997-04-09)
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