Empirical Evidence for SOC Dynamics in Software Evolution

We examine eleven large open source software systems and present empirical evidence for the existence of fractal structures in software evolution. In our study, fractal structures are measured as power laws throughout the lifetime of each software system. We describe two specific power law related phenomena: the probability distribution of software changes decreases as a power function of change sizes; and the time series of software change exhibits long range correlations with power law behavior. The existence of such spatial (across the system) and temporal (over the system lifetime) power laws suggests that self-organized criticality (SOC) occurs in the evolution of open source systems. As a result, SOC may be useful as a conceptual framework for understanding software evolution dynamics (the cause and mechanism of change or growth). We also discuss the implications of SOC to software practices.