A logical system involving theory of classes, developed by Stanislaw Lesniewski (1886-1939).
A structure of concepts or entities within a domain, organized by relationships; a system model.
The theory of a particular philosopher or school of thought concerning the fundamental types of entity in the universe.
The branch of metaphysics that addresses the nature or essential characteristics of being and of things that exist; the study of being qua being.
In a subject view, or a world view, the set of conceptual or material things or classes of things that are recognised as existing, or are assumed to exist in context, and their interrelations; in a body of theory, the ontology comprises the domain of discourse, the things that are defined as existing, together with whatever emerges from their mutual implications.