Measuring software sustainability

Planning and management of software sustainment is impaired by a lack of consistently applied, practical measures. Without these measures, it is impossible to determine the effect of efforts to improve sustainment practices. In this paper we provide a context for evaluating sustainability and discuss a set of measures developed at the Software Engineering Institute at Carnegie Mellon University.

1. Introduction

Management of sustainment teams and organizations is inadequately supported by existing measures in that these measures cannot be readily applied to improving system sustainability or in evaluation. For example, a common maintainability measure is mean time to repair (MTTR) [Fenton 91] MTTR may be used, for example, to reduce turn-around times. On the surface this appears to be a worthy goal. However, if measuring MTTR encourages developers to rush fixes resulting in additional downstream defects, these efforts may actually reduce the overall sustainability of the system. Tracking the rate at which modification requests are submitted is also problematic. A low submission rate may reflect user dissatisfaction that an existing backlog of requests has not been satisfied rather than an indicator of increased product quality.