Characterization of functional software requirements space: The law of requirements taxonomic growth

This paper reports on a large-scale empirical multiple-case study that aimed to characterize the requirements space in the domain of web-based Enterprise Systems (ES). Results from this study, among others, showed that, on the average, about 85% of all the software functionalities in the studied domain are specified using a small core set of five requirements classes even though the results of the study hint at a larger set of nine requirements classes that should be covered. The study also uncovered a law describing the growth pattern of the emerging requirements classes in software domains. According to this law, the emergence of the classes in a requirements taxonomic scheme for a particular domain, independent of the order in which specifications of requirements in that domain are analyzed, includes a rapid initial growth phase, where the majority of the requirements classes are identified, followed by a rapid slow-down phase with periods of no growth (i.e., the stabilization phase).