Mechanism of asymmetric software structures: A complex network perspective from behaviors of new nodes

Studying the function call graphs in complex software can provide significant insights into the software evolution process. We found node in- and out-degree distributions asymmetric in the call graphs of 223 versions of Linux kernel modules (V1.1.0 to V2.4.35). Nodes newly introduced in these modules tended to attach to themselves (clustering) and existing high in-degree nodes. We proposed the αβ Model to generate call graphs for different kernel modules. The model preserved asymmetry in the degree distributions and simulated the new node behaviors. Last, we discussed how the αβ Model could be used effectively to study the robustness of complex networks.