Enhanced n-version programming and recovery block techniques for web service systems

In recent years, web services (WS’s) have been widely used to support interoperable machine-to-machine interaction over a network. In order to ensure a reliable WS system, a number of fault tolerance designs have been proposed. It is known that network connection and hardware devices may fail. In addition, the acceptance test (AT) as well as the decision mechanism (DM), which are common in fault tolerance designs, could also fail unexpectedly. Such uncertainties may affect the reliability of a WS-based system but have not yet been carefully considered in reliability modeling. Therefore, we propose extended NVP (ENVP) and extended RB (ERB) for the reliability analysis. Various operations of ENVP and ERB are discussed, and a simulation procedure is implemented to evaluate the system reliability and the failure probability of fault-tolerant WS-based systems. The experimental results show a high degree of correlation between the numbers of AT’s and the reliability improvements. The proposed fault tolerance designs could improve the system reliability, and the simulation procedure could also help in exploring appropriate configurations of fault tolerance designs for practitioners.