Restructuring software to improve its design can lower software maintenance costs. One problem encountered during restructuring is formulating the new design. A meaning-preserving program restructuring tool with a star diagram manipulable visualization can help a programmer redesign a program based on abstract data types. However, the transformational support required for meaning-preserving restructuring is costly to provide. Also, programmers encounter comprehension and recall difficulties in complex restructuring tasks. Consequently, transformations were replaced with visual and organizational aids that help a programmer to plan and carry out a complex restructuring. For example, a star diagram manipulation called trimming was added, which mimics the way that basic restructuring transformations affect the star diagram display, allowing a programmer to plan a restructuring without depending upon restructuring transformations. With the ability to annotate trimmed star diagram components, plans can be recorded and later recalled. Programmer-controlled elision was added to help remove clutter from star diagram views. We implemented a star diagram planning tool for C programs, measured its elision capabilities, and performed a programmer study. We found that elision is effective in controlling star diagram size, and the study revealed that each programming team successfully planned its restructuring in rather different, unanticipated ways. These experiments resulted in important improvements in the tool's software design and user interface.

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 performed 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. In the study we found that each programming team successfully planned their restructuring in rather different, unanticipated ways.