We provide a formal agenda for teaching the object-oriented paradigm in a programming language independent manner, and a tool which supports our teaching approach. Our proposal for a comprehensive study of the subject includes an ordered set of objectives designed to guide the uninitiated user from zero knowledge about object-oriented programming through class definitions, inheritance, subtyping, and the parameterization of classes. This set of graded objectives provides both a useful metric for gauging a student's progress, and a facility through which users can begin their studies at a level commensurate with their experience.

We introduce a simple, programming language independent rule (known in-house as the Law of Demeter™) which encodes the ideas of encapsulation and modularity in an easy to follow form for the object-oriented programmer. You tend to get the following related benefits when you follow the Law of Demeter while minimizing simultaneously code duplication, the number of method arguments and the number of methods per class: Easier software maintenance, less coupling between your methods, better information hiding, narrower interfaces, methods which are easier to reuse, and easier correctness proofs using structural induction. We discuss two important interpretations of the Law (strong and weak) and we prove that any object-oriented program can be transformed to satisfy the Law. We express the Law in several languages which support object-oriented programming, including Flavors, Smalltalk-80, CLOS, C++ and Eiffel.