Evaluating Lehman's Laws of software evolution within software product lines industrial projects

The evolution of a single system is a task where we deal with the modification of a single product. Lehman's Laws of software evolution were broadly evaluated within this type of system and the results shown that these single systems evolve according to his stated laws over time. However, considering Software Product Lines (SPL), we need to deal with the modification of several products which include common, variable, and product specific assets. Because of the several assets within SPL, each stated law may have a different behavior for each asset kind. Nonetheless, we do not know if all of the stated laws are still valid for SPL since they were partially evaluated in this context. Thus, this paper details an empirical investigation where Lehman's Laws (LL) of Software Evolution were used in two SPL industrial projects to understand how the SPL assets evolve over time. These projects are related to an application in the medical domain and another in the financial domain, developed by medium-size companies in Brazil. They contain a total of 71 modules and a total of 71.442 bug requests in their tracking system, gathered along the total of more than 10 years. We employed two techniques - the KPSS Test and linear regression analysis, to assess the relationship between LL and SPL assets. Results showed that one law was completely supported (conservation of organizational stability) for all assets within both empirical studies. Two laws were partially supported for both studies depending on the asset type (continuous growth and conservation of familiarity). Finally, the remaining laws had differences among their results for all assets (continuous change, increasing complexity, and declining quality). (C) 2016 Elsevier Inc. All rights reserved.