Quantifying the Encapsulation of Implemented Software Architectures

Applying encapsulation techniques lead to software systems in which the majority of changes are localized, which reduces maintenance and testing effort. In the evaluation of implemented software architectures, metrics can be used to provide an indication of the degree of encapsulation within a system and to serve as a basis for an informed discussion about how well-suited the system is for expected changes. Current literature shows that over 40 different architecture-level metrics are available to quantify the encapsulation, but empirical validation of these metrics against changes in a system is not available. In this paper we investigate twelve existing architecture metrics for their ability to quantify the encapsulation of an implemented architecture. We correlate the values of the metrics against the ratio of local change over time using the history of ten open-source systems. In the design of our experiment we ensure that the values of the existing metrics are representative for the time period which is analyzed. Our study shows that one of the suitable architecture metrics can be considered a valid indicator for the degree of encapsulation of systems. We discuss the implications of our findings both for the research into architecture-level metrics and for software architecture evaluations in industry.