Visualizing Co-Change Information with the Evolution Radar

Software evolution analysis provides a valuable source of information that can be used both to understand a system's design and predict its future development. While for many program comprehension purposes, it is sufficient to model a single version of a system, there are types of information that can only be recovered when the history of a system is taken into account. Logical coupling, the implicit dependency between software artifacts that have been changed together, is an example of such information. Previous research has dealt with low-level couplings between files, leading to an explosion of the data to be analyzed, or has abstracted the logical couplings to the level of modules, leading to a loss of detailed information. In this paper, we present a visualization-based approach that integrates logical coupling information at different levels of abstraction. This facilitates an in-depth analysis of the logical couplings, and at the same time, leads to a characterization of a system's modules in terms of their logical coupling. The presented approach supports the retrospective analysis of a software system and maintenance activities such as restructuring and redocumentation. We illustrate retrospective analysis on two large open-source software systems.