A cost model for software maintenance & evolution

The purpose of this essay is to present a costing model for software maintenance and evolution based on a separation of fixed and variable costs. There has always been a problem in distinguishing between the maintenance activities covered by the standard maintenance fee and those charged extra to the user. Separating these two types of costs is essential to every maintenance operation to prevent costs from getting out of control. In this paper the author proposes a solution, which can lead to better cost estimations and a financially more stable maintenance operation. Particular emphasis is placed on a sharp division between work done to maintain the system functionality as it is and work done to enhance that functionality.