Additive reliability model for the analysis of modular software failure data

Most software reliability models are applicable to a single piece of software. For more complex systems, Markov models have been studied assuming that complete reliability information at the module level is available. In this paper, we study an additive model which assumes that each subsystem or module undergoes independent testing and the reliability of the complete system has to be assessed. Subsystem reliabilities are estimated and the system reliability is assessed using the additive model. The approach is simple, but generic in a sense that existing models can be combined. An example is also presented based on the log-power model, a model with simple graphical interpretation, and it shows that the modular information should be used for system reliability assessment whenever such information is available.