Structural evolution of an open source system: a case study

Software evolution empirical studies are made possible only when data is available and easily collectable. Open source software provides a good opportunity for observing software products in various phases of their evolution, growth and maturity. One of the aspects that have not been analyzed yet through empirical studies is the relation that exists between code components growth and the evolving code structure. In this paper, we look at the growth of code elements by measuring the total number of files per release and also by visualizing the folder structure as a tree. Both, the number of files and the shape of the folder tree structure offer proxies to study the evolving complexity of the system. In this study, a number of hypotheses about the evolutionary patterns in the size of files and folders, in the folder tree structure, reflecting common assumptions on software engineering and open source are tested against empirical data reflecting the evolution of the ARLA system. We also relate some of the observed patterns to the arrival rate of new developers. Results show that the number of code components (files and folders) over releases can be interpreted as a linear trend with a superimposed ripple. We also describe the more apparent characteristics of the evolution of the folder tree structure. Furthermore, we observe that the average size of files and folders tends to stabilize over releases. The cumulative number of people who have been involved as developers of the system follows a trend which resembles that of the size in files over releases, suggesting that the latter could provide a good indicator for rate of work and productivity. There was no apparent relation between the arrival rate of developers and the changes observed in the code structure.