Model-based Software Cost Estimation: Calculating Time and Effort for Software Evolution Projects

Abstract

Estimating the costs of an evolution project differs from development project estimation and must follow its own rules. When estimating development project costs the whole system is taken into consideration. When estimating evolution costs only those parts of the system are considered that have to be changed or added. The rest is left as it is, but must be included in the test. The mixing of changed components with new components and old components presents several challenges to software product management. The main challenge is how to recognize those features that have to be added or changed – feature analysis. Together they make up the change domain. The extent of this change domain is the key factor in estimating the costs of change in each new release. It is measured by means of one or more size metrics such as function-points, data-points and object-points in order to convert size into effort. The approach used here was to model the change requirements and then compare the change model with the original requirements model to ascertain the scope of the change. To this end, both the original and the current requirements had to be extracted from the requirement text and then modelled. This approach was applied here to calculate the costs of expanding a national health record system. The preliminary results are presented in this short paper.