Layered explanations of software: a methodology for program comprehension

In dealing with the legacy systems, one often encounters poorly documented and heavily maintained software. Lack of understandability of these systems complicates the task of software maintenance, making it time consuming and limiting the possibilities of the evolution of the system. We present a methodology that helps the programmers to understand programs. Our approach is compatible with the "top-down theory" of software understanding, where the programmer creates a chain of hypotheses and subsidiary hypotheses, concerning the properties of the code. Then he/she looks for evidence (beacons) in the code. Our approach shortens the process of hypotheses creation and verification, and allows recording of successful hypotheses for the future maintenance. All information needed for understanding is recorded in layers of annotations. An experiment was conducted to investigate how the proposed methodology helps in program understanding. A tool supporting the methodology, is presented.<>