This paper describes some of the difficulties that may be expected in the maintenance of software developed using the new object oriented languages. The concepts of inheritance and of polymorphism provide the great strengths of these languages, but they also introduce difficulties in program analysis and understanding. The paper analyzes problems of dynamic binding, object dependencies, dispersed program structure, control of polymorphism, high-level understanding, and detailed code understanding. Examples are presented based on code from a PC Smalltalk environment and from studies of two systems under development at Bell Communications Research

Some of the difficulties that may be expected in the maintenance of software developed using the new object oriented languages are described. The concepts of inheritance and of polymorphism provide the great strengths of these languages but they also introduce difficulties in program analysis and understanding. The authors analyze problems of dynamic binding, object dependencies, dispersed program structure, control of polymorphism, high level understanding and detailed code understanding. Examples are presented based on code from the Smalltalk V environment. Recommendations are made for possible tool support, particularly using the concepts of dependency analysis, external dependency graphs, and clustering methodologies. Some suggestions are made concerning maintenance in firefighting situations, when a failed system must be brought back into service with a minimum of lost time.>

A general-purpose toolset that is being developed to capture and analyze software dependencies is described. The tools are designed to serve as reusable components. They can be used not only to aid programmers directly in understanding programs but also as a basis from which other specialized tools can be constructed. The tools use the concept of a dependency graph as a basic abstraction to simplify the understanding of software relationships. Definitional, calling, functional and data-flow dependencies are analyzed. An external dependency graph for each function is developed to encapsulate the effects of function cells.>