Notes to the Reviewers

An essential characteristic of large scale software development is parallel development by teams of developers. How this parallel development is structured and supported has a profound e ect on both the quality and timeliness of the product. We conduct an observational case study in which we collect and analyze the change and con guration management history of a legacy system to delineate the boundaries of, and to understand the nature of, the problems encountered in parallel development. The results of our studies are 1) that the degree of parallelism is very high{higher than considered by tool builders; 2) there are multiple levels of parallelism and the data for some important aspects are uniform and consistent for all levels; 3) the tails of the distributions are long, indicating the tail, rather than the mean, must receive serious attention in providing solutions for these problems; and 4) there is a signi cant correlation between the degree of parallel work on a given component and the number of quality problems it has. Thus, the results of this study are important both for tool builders and for process and project engineers.