The Impact of Complexity on Software Design Quality and Costs: An Exploratory Empirical Analysis of Open Source Applications

It is well known that complexity affects software development and maintenance costs. In the Open Source context, the sharing of development and maintenance effort among developers is a fundamental tenet, which can be thought as a driver to reduce the impact of complexity on maintenance costs. However, complexity is a structural property of code, which is not quantitatively accounted for in traditional cost models. This paper introduces the concept of functional complexity, which weights the well-established McCabe's cyclomatic complexity metric to the number of interactive functional elements that an application provides to users. Such metric is used to analyze how Open Source development costs are affected by complexity. Traditional cost models, like CoCoMo, do not take into account the impact of complexity in estimating costs by means of accurate indicators. In contrast, results show how a higher complexity is associated with a lower design quality of code, and, hence, higher maintenance costs. Consequently, results suggest that a reliable effort estimation should be based on a precise evaluation of software complexity. Analyses are based on quality, complexity, and maintenance effort data collected for 59 Open Source applications (corresponding to 906 versions) selected from the SourceForge.net repository.