Optimal reliability allocation problem for a modular software system

This paper addresses the problem of optimal selection of components for a modular software system that is built by assembling a set of Commercial Off-The-Shelf (COTS) components and/or independent programs developed within the organization. For each module more than one alternative component is available and the same alternative can be purchased at a higher price if greater reliability is desired. It is also assumed that redundant component can be added in the modules to achieve fault tolerance. Now the problem is how to select the components, so as to maximize the system reliability. The first optimization model proposed in this paper maximizes the system reliability incorporating redundancy at component level with budgetary constraints. In the second model the issue of compatibility among alternatives available for different modules, is accounted for. Numerical illustrations are provided to demonstrate the models developed in this paper.