Software-reliability growth model: primary-failures generate secondary-faults under imperfect debugging

Little work has been done on extending existing models with imperfect debugging to the more realistic situation where new faults are generated from unsuccessful attempts at removing faults completely. This paper presents a software-reliability growth model which incorporates the possibility of introducing new faults into a software system due to the imperfect debugging of the original faults in the system. The original faults manifest themselves as primary failures and are assumed to be distributed as a nonhomogeneous Poisson process (NHPP). Imperfect debugging of each primary failure induces a secondary failure which is assumed to occur in a delayed sense from the occurrence time of the primary failure. The mean total number of failures, comprising the primary and secondary failures, is obtained. The authors also develop a cost model and consider some optimal release-policies based on the model. Parameters are estimated using maximum likelihood and a numerical example is presented