Using Service Utilization Metrics to Assess and Improve Product Line Architectures

Metrics have long been used in software engineering to measure, evaluate, and improve software products and processes. Many metrics have been developed and their subsequent use in different settings has led to varying levels of success. Software architecture is a discipline in which few metrics have been applied, a surprising fact given the important role that software architecture plays in software development. Software product line architectures represent one area of software architecture in which metrics can be of especially great use. The critical importance of the structure defined by a product line architecture requires that its properties be meaningfully assessed and that informed architectural decisions be made to guide its evolution. In this paper, we present several novel metrics that we have designed to address this issue. These metrics are based on the concept of service utilization and are designed to take into account the context in which individual architectural elements are placed. We show the utility of the metrics by applying them in a case study involving a digital library product line architecture. In doing so, we demonstrate how the metrics illustrate deficiencies that, when addressed, improve the overall structural quality of the product line architecture.