A micro software reliability model for prediction and test apportionment

A discussion is given on a new micro model which allows reliability estimation to begin at the module test phase, continue during integration testing and carry over to field deployment. The model first decomposes the structure of the software into a set of execution paths. The failure rate of the software system is related to the frequency and time of path traversal, and the probability of encountering an error during traversal. A second stage of decomposition is necessary to relate the path reliability to the module reliabilities. In the second decomposition the failure probabilities are expressed by combinatorial expressions involving the probabilities of failure of the individual modules. Since the basic model decomposes the structure into execution paths the model can be used to apportion reliabilities and test efforts among the various execution paths. The optimum allocation is computed for a particular effort model and applied to a numerical example