In this paper, existing software reliability models based on an nonhomogeneous Poisson process (NHPP) are summarized. A recently developed NHPP model with imperfect debugging and time-dependent fault detection rate is examined. T he results show that this proposed model provides improved descriptive and predictive power when compared with other existing NHPP models. T he model can also be incorporated into a software cost model for reliability assessment. T he optimal release policies which minimize the expected total software cost is also presented.
Nomenclaturea…t † time-dependent fault content function b…t † fault detection rate per unit of time C 1 testing cost coe cient, that is software testing cost per unit time C 2 error removal cost coe cient, that is cost of removing a fault per unit time during testing phase C 3 risk cost coe cient, risk cost due to software failure m…t † mean value function, that is expected number of faults detected by time t m…t k † estimated cumulative number of failures at time t k obtained from the model R…x=t † software reliability function, that is conditional probability that no faults occur during …t;t ‡ x † given that the last failure occurred at time t y k total number of failures observed at time t k according to the actual data P k sum over k from 1 to n
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