A systematic arrangement of all of the important categories of objects or concepts which exist in some field of discourse, showing the relations between them. When complete, an ontology is a categorization of all of the concepts in some field of knowledge, including the objects and all of the properties, relations, and functions needed to define the objects and specify their actions. A simplified ontology may contain only a hierarchical classification (a taxonomy) showing the type subsumption relations between concepts in the field of discourse. An ontology may be visualized as an abstract graph with nodes and labeled arcs representing the objects and relations.

(32NN) A model of how to specify a subject area of interest in which concepts, their attributes, and relationships (associations between concepts) are explicitily named and distinguished. Constraints stipulate distinctions that differentiate concepts, governing how they participate in relationships, and how implicit knowledge is made explicit through qualifiers that allow inferencing over relationships properties. A standard language for representing an ontology on the web is the W3C standard OWL. (329E) See W3C Semantic Web Website (329F)

A vocabulary and set of agreed upon definitions to describe a subject domain. The general subject area of reactive, real-time systems does not have an ontology. However, the various subfields all have their own ontologies. e.g., this glossary. Note that this definition is a good bit narrower than what a philosopher would likely take to be an ontology.

The creation of a systematically ordered data structure that enhances exchange of information between computers and scientists. Ontologies enable the definition and sharing of domain-specific vocabularies.

That department of the science of metaphysics which investigates and explains the nature and essential properties and relations of all beings, as such, or the principles and causes of being.

The branch of philosophy that is concerned with basic questions about reality and existence.

The branch of metaphysics concerned with the question of the sorts of things that exist.

the collection of distinct entities that is considered to exist within a particular view of a portion of the universe.

a coherent set of definitions of terms (in KIF, relation, function, or object constants) including axioms constraining their usage and meaning, and English text decribing it for humans

a collection of descriptions of the world that helps us define the meaning of our experience and actions

a logical theory that constrains the indended models of a logical language

The high level definitions of the objects, their actions, and behavior in a system. Sometimes objects are defined by their noun phrases and their actions defined by their verb phrases, while their behavior is defined by the communications.