Scale-Free Nature of Java Software Package, Class and Method Collaboration Graphs

Software collaboration graphs for two Open Source software projects written in the Java programming language, the Kowari Metastore and JRDF, were analyzed for fifteen-month periods of development. Collaboration graphs were produced at the package, class and method levels. The collaboration graphs were found to form networks which exhibited approximately scale-free properties at all three levels and during each period analyzed. This finding tends to support claims made by others that software class collaboration graphs approximate scale-free networks and provides new insights that they seem to retain the scale-free properties across different levels of granularity and over the course of their development life cycle. Significant differences between the magnitudes of power law exponents identified and those found in C and C++ applications by previous researchers are noted and discussed. Specifically, only the method-level collaboration graphs were found to have power law exponents in the most common range for scale-free networks (2 < γ < 3).