Multistage Growth Model for Code Change Events in Open Source Software Development: An Example Using Development of Nagios

In recent years, many open source software (OSS) products have become popular and widely used in the information technology (IT) business. To successfully run IT business, it is important to properly understand the OSS development status. Having a proper understanding of development status is necessary to evaluate and predict the product quality. However, the OSS development status is not easy to understand, because it is often concurrently developed by many distributed contributors, and its developmental structure is complicated. To aid the understanding of the development status, there is an approach that models the trend of source code change events (evolution) with a growth curve. Although an application of growth curves seems to be a promising approach, there has been a big issue that a single growth curve is often unsuitable for modeling the whole evolution because of its complex evolutionary behavior. This paper proposes a multistage model that divides the whole development period into some stages, and applies a different growth curve to a different stage. The empirical investigation in this paper shows that the switching points of stages have meaningful associations with the release dates.