Æliens

This chapter treats polymorphism from a foundational perspective. It characterizes abstract inheritance as employed in knowledge representation and proceeds with a formal definition of the subtype relation, culminating in a family of calculi for a type theoretical analysis of the constructs employed in object-oriented programming. The features studied include generic types, overloading, data hiding and self-references.

Due to the formal background needed, the project assignments listed below have the flavor of research projects and must be considered for advanced students only. Possible assignments are

• designing a language incorporating both knowledge representation features and objects,
• the development of a type calculus for a concrete programming language, such as Smalltalk, Eiffel, C++, or Java
• the development of a type checker for a variety of polymorphic constructs.

Since some of this work has already be done (see below), one may simply advise students to study these efforts.