Exploring the Structure of Complex Software Designs: An Empirical Study of Open Source and Proprietary Code

This paper reports data from a study that seeks to characterize the differences in design structure between complex software products. We use design structure matrices (DSMs) to map dependencies between the elements of a design and define metrics that allow us to compare the structures of different designs. We use these metrics to compare the architectures of two software products--the Linux operating system and the Mozilla Web browser--that were developed via contrasting modes of organization: specifically, open source versus proprietary development. We then track the evolution of Mozilla, paying attention to a purposeful "redesign" effort undertaken with the intention of making the product more "modular." We find significant differences in structure between Linux and the first version of Mozilla, suggesting that Linux had a more modular architecture. Yet we also find that the redesign of Mozilla resulted in an architecture that was significantly more modular than that of its predecessor and, indeed, than that of Linux. Our results, while exploratory, are consistent with a view that different modes of organization are associated with designs that possess different structures. However, they also suggest that purposeful managerial actions can have a significant impact in adapting a design's structure. This latter result is important given recent moves to release proprietary software into the public domain. These moves are likely to fail unless the product possesses an "architecture for participation."