Measurement of functional reuse in maintenance

This paper is concerned with the identification and measurement of reuse within projects in which functional enhancements have been added to existing software applications. The proposed approach is based on the measurement of reuse from a functional perspective rather than from a technical perspective. Two key concepts are introduced: a reuse indicator and a predictor ratio. The reuse indicator is derived from an analysis of the function types as currently defined in Function Points Analysis. The predictor ratio is derived from an understanding of the avoided-cost concept and of how it can be captured using historical databases of function points from previous development projects. This paper indicates how, in functional enhancement projects, the predictor ratio can be combined into the reuse indicator to derive an alternative size measure which takes into account functions reused and not redeveloped. The paper also demonstrates how these ratios can then be integrated in a maintenance productivity model to analyse the benefits of reuse by taking into account the avoided cost of functions reused. A case study based on an industrial data set is provided to illustrate the measurement of functional reuse in an enhancement project and its impact in maintenance productivity analysis.