Maintenance and testing effort modeled by linear and nonlinear dynamic systems

Maintenance and testing activities - conducted, respectively, on the releas e currently in use/to be delivered - absorb most of total lifetime cost of software development. Such economic relevance suggests investigating the ma intenance and testing processes to find models allowing software engineers to better estimate, plan and manage costs and activities. Ecological systems in which predators and prey compete for surviving were i nvestigated by applying suitable mathematical models. An analogy can be dra wn between biological prey and software defects, and between predators and programmers. In fact, when programmers start trying to recognize and correc t code defects, while the number of residual defects decreases, the effort spent to find any new defect has an initial increase, followed by a decline , when almost all defects are removed, similar to prey and predator populat ions. This paper proposes to describe the evolution of the maintenance and testin g effort by means of the predator-prey dynamic model. The applicability of the model is supported by the experimental data about two real world projec ts. The fit of the model when parameters are estimated on all available dat a is high, and accurate predictions can be obtained when an initial segment of the available data is used for parameter estimation. (C) 2001 Elsevier Science B.V. All rights reserved.