Tools for preventive maintenance of software which is written following the object-oriented paradigm are discussed. A set of guidelines, called the Law of Demeter is described, and its implications for software maintenance are discussed (K.J. Lieberherr, I. Holland, 1989). The advantages of grammar-based object-oriented design and programming for software maintenance are discussed. Two kinds of grammar-based maintenance tool are studied: class evolution tools, especially an automatic class parameterization tool and growth plan tools with applications to software maintenance planning and regression testing.>

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.