The chapter describes models, called notional models, which are based on primary mental abstractions: identification, generalization, and association. The process of abstraction does not depend on any subject domain, but is determined only by the abilities of the cognizing human. A notional model consists of a notional structure and contents of notions. The notional structure describes each notion as a set of other notions united by one of the mental abstractions. The content of notions is described using various enumerating and resolving procedures. Refusal to describe associations as links between concepts makes the notional model semantically invariant, improves the transparency of notional models, and allows you to create intelligent information systems with a linear or logarithmic estimate of query execution time. These effects are because associations between notions are notions. Another difference between the conceptual and the notional models is the description of notions in several aspects simultaneously.