How do program understanding tools affect how programmers understand programs?

We explore the question of whether program understanding tools enhance or change the way that programmers understand programs. The strategies that programmers use to comprehend programs vary widely. Program understanding tools should enhance or ease the programmer's preferred strategies, rather than impose a fixed strategy that may not always be suitable. We present observations from a user study that compares three tools for browsing program source code and exploring software structures. In this study, 30 participants used these tools to solve several high level program understanding tasks. These tasks required a broad range of comprehension strategies. We describe how these tools supported or hindered the diverse comprehension strategies used.