Analyzing the Evolution of Large-Scale Software Systems Using Design Structure Matrices and Design Rule Theory: Two Exploratory Cases

Designers have long recognized the value of modularity, but important software modularity principles have remained informal. According to Baldwin and Clark's (2000) design rule theory (DRT) , modular architectures add value to system designs by creating options to improve the system by substituting or experimenting on individual modules. In this paper, we examine the design evolution of two software product platforms through the modeling lens of DRT and design structure matrices (DSMs). We show that DSM models and DRT precisely explain how real- world modularization activities in one case allowed for different rates of evolution in different software modules and in another case conferred distinct strategic advantages on a firm by permitting substitution of an at-risk software module without substantial change to the rest of the system. Our results provide positive evidence that DSM and DRT can inform important aspects of large-scale software structure and evolution, having the potential to guide software architecture design activities.