Before making a change to a system, software developers typically explore the source code to find and understand the subset relevant to their task. Software changes often involve code addressing different conceptually-related segments of the implementation (concerns), which can be scattered across multiple modules. These scattered concerns make it difficult to reason about the code relevant to a change. We carried out a study to investigate how developers discover and manage scattered concerns during a software evolution task, and the role that structural queries play during the investigation. The task we studied consists of a developer adding a feature to a 65kloc Java code base. The study involved eight subjects: four who were not briefed about scattered concerns, and four who were trained to use a concern-oriented investigation tool. Analysis of the navigation among the different program elements examined by the subjects during the task shows evidence that, independent of whether concern-oriented tool support was available, the most successful subjects focused on specific concerns when planning their task, and used a high proportion of structural queries to investigate the code. In addition to the study results, this paper introduces two novel analyses: navigation graphs, which support the analysis of a subject's behavior when investigating source code, and variant analysis, which is used for evaluating the results of a program evolution task.
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