Economic allocation of target reliability in modular software systems

This paper proposes a cost model for allocation of component failure intensities to achieve a software system's reliability target while minimizing the cost in the design phase. Specifically, the objective of allocation is to distribute effort among software components to facilitate cost-effective progress towards a system reliability goal. The economic model presented is a function of a component's failure intensity. This model includes a cost component reflective of the costs to restore a field failure and customer loss due to system unavailability. In this paper, usage time of a module is used as a weight factor that affects allocation. This weight factor represents the importance of increasing the reliability of a module and is derived from operational profiles. The methodology proposed provides a basic approach to optimization of reliability allocation, subject to reliability constraints. A numerical example is presented to illustrate the application of the proposed economic model.