The CRSS Metric for Package Design Quality

Package design is concerned with the determining the best way to partition the classes in a system into subsystems. A poor package design can adversely affect the quality of a software system. In this paper we present a new metric, Class Reachability Set Size (CRSS), the distribution of which can be used to determine if the relationships between the classes in a system preclude it from a good package design. We compute CRSS distributions for programs in a software corpus in order to show that some real programs are precluded in this way. Also we show how the CRSS metric can be used to identify candidates for refactoring so that the potential package structure of a system can be improved.