Intension, Extension, and Type Hierarchies

Intension versus extension

The intension of an object type is given by the set of its features, this includes attributes, associations, constraints, and operations. The extension of an object type is the set of all objects that instantiate the object type. The extension of an object type is also called its population.

All features of a supertype are included in the intensions or feature sets, of its subtypes (intensional inclusion). All instances of a subtype are included in the extensions, or instance sets, of its supertypes (extensional inclusion).

Due to this duality intension and extension, we can specialize a ...