Predicting decay in program modules of legacy software systems

Legacy software systems may go through many releases. It is important to ensure that the reliability of a system improves with subsequent releases. Methods are needed to identify decaying software modules, i.e., modules for which quality decreases with each system release. Early identification of such modules during the software life cycle allows us to focus quality improvement efforts in a more productive manner, by reducing resources wasted for testing and improving the entire system. We present a scheme to classify modules in three groups---Decayed, Improved, and Unchanged---based on a three-group software quality classification method. This scheme is applied to three different case studies, using a case-based reasoning three-group classification model. The model identifies decayed modules, and is validated over different releases. The main goal of this work is to focus on the evolution of program modules of a legacy software system to identify modules that are difficult to maintain and may need to be reengineered.