Software quality and reliability prediction: a time-dependent model with controllable testing coverage and repair intensity

In a previous paper, the defect detection and removal rates in a given project were mathematically modeled by the author (Proc. COMPSAC 87, p.340-6, Oct. 1987). Contrary to other models, the author´s model was a comprehensive birth-death model that was triggered by faults introduced through code submission. The repair process removed the detected defects while reintroducing new defects at a certain rate. Homogeneous statistical distributions were used to produce the model. In the present study, two important improvements are introduced, namely, the concepts of time-varying test coverage and of time-varying defect repair intensity. The test coverage and the repair intensity are increasing functions of the software coverage by the test program and the resource availability for defect repairs, respectively. The modeling of these two concepts provides a better tie of the model to reality. Nonhomogeneous distributions provide the necessary mathematical tool