They develop a theory of situations and of meaning as a relation between situations. The theory provides a system of abstract objects that makes it possible to describe the meaning of both expressions and mental states in terms of the information they carry about the external world. Two major concepts of Situation Theory are infons and situations. Infons are the basic informational units. They should be considered as discrete items of information.
Situations are first-class citizens of the theory, and are defined intensionally.
Given a real situation s , the set is the corresponding abstract situation. One important paradigm behind Situation Theory is a schema of individuation , a way of carving the world into uniformities. The notions of individual, relation, spatial and temporal location, and further entities depend upon this schema of individuation. Thus, constituents of Situation Theory such as infons, constraints, and situations are determined by the agent's schema of individuation. Object types are determined over some initial situation.