The research described in this thesis addresses itself to the problem of maintaining large, undocumented systems written in languages that contain a module construct. Emphasis is placed on developing techniques for analysing the code of these systems, thereby helping a maintenance programmer to understand a system. Techniques for improving the structure of a system are presented. These techniques help make the code of a system easier to understand. All the code analysis techniques described in this thesis involve reasoning with, and manipulating, graphical representations of a system. To help with these graph manipulations, a set of graph operations are developed that allow a maintenance programmer to combine graphs to create a bigger graph, and to extract subgraphs from a given graph that satisfy specified constraints. A relational database schema is developed to represent the information needed for inter-module code analysis. Pointers are given as to how this database can be used for inter-module code analysis
