noun. The branch of metaphysics that deals with the nature of being.

noun. The theory of being; that branch of metaphysics which investigates the nature of being and of the essence of things, both substances and accidents.

noun. 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.

noun. 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.

noun. The branch of metaphysics that addresses the nature or essential characteristics of being and of things that exist; the study of being qua being.

noun. The theory of a particular philosopher or school of thought concerning the fundamental types of entity in the universe.

noun. A logical system involving theory of classes, developed by Stanislaw Lesniewski (1886-1939).

noun. A structure of concepts or entities within a domain, organized by relationships; a system model.

noun. (computer science) a rigorous and exhaustive organization of some knowledge domain that is usually hierarchical and contains all the relevant entities and their relations

noun. the metaphysical study of the nature of being and existence