Understanding large-scale software-a hierarchical view

Program comprehension accounts for a large portion of software development costs and effort. The academic literature contains research on program comprehension of short code snippets, but comprehension at the system level is no less important. We claim that comprehending a software system is a distinct activity that differs from code comprehension. We interview experienced developers, architects, and managers in the software industry and open-source community, to uncover the meaning of program comprehension at the system level. The interviews demonstrate, among other things, that system comprehension is detached from code and programming language, and includes scope that is not captured in the code. It focuses on the structure of the system and less on the code itself. This is a continuous, iterative process, which mixes white-box and black-box approaches at different layers of the system, and combines both bottom-up and top-down comprehension strategies.