A Hierarchical Program Representation for Refactoring

Currently there is a lot of interest in graph representations of software systems, as they provide a natural and flexible means to describe complex structures. The various visual sublanguages of the UML are perhaps the most obvious example of this. In [10] a graph representation of object-oriented programs was presented that enables one to describe refactoring operations (behaviour-preserving changes in the structure of a program) in a formal, concise way by graph rewriting productions. In general, however, a refactoring makes changes to a small part of a program, so the graph representation should only contain the information needed to carry out that refactoring. All other details are redundant and make the graph unnecessarily large for good visualization. A possible solution consists in using a hierarchical representation. Such a representation of object-oriented programs is presented in this paper. It is based on node-rewriting graph productions: each refinement step corresponds to a production. The construction is illustrated by applying it to a small Java simulation of a Local Area Network.