Support for Planning the Restructuring of Data Abstractions in Large Systems

Restructuring software to improve its design can lower software maintenance costs. One problem in carrying out such a restructuring is planning the new detailed design. The star diagram manipulable visualization can help a programmer redesign a program based on abstract data types. However, our measurements revealed that the view can be too large for a programmer to effectively assimilate. Also, design plans can be expressed only by restructuring, although our studies revealed that it is beneficial to preplan a restructuring. Finally, the tool user can build a star diagram for only a single data structure, although an abstract data type might actually have several components or have multiple instantiations. Exploiting basic properties of the star diagram can mitigate these problems. First, programmer-controlled elision can remove clutter from the star diagram view. Second, elision and annotation of star diagram components can mimic restructuring, thereby supporting the planning of a restructuring. Such support also allows for the planning of a non-restructuring maintenance task. Finally, to dynamically control what data structures are visualized, the tool user can union star diagrams. We built a star diagram planning tool for C programs, measured its elision capabilities, and perfomed a programmer study for the encapsulation of a widely-used data structure in a 28,000 line program. We found that the amount of elision can be substantial, but is not always adequate....