LAUSR

When combining several services into a composite service, it is non-trivial to determine, prior to service deployment, performance and reliability values of the composite service. Moreover, once the service is deployed, it is often the case that during operation it fails to meet its service-level agreement (SLA) and one needs to detect what has gone wrong (i.e., performance/reliability bottlenecks). To study these issues, we develop a Semi-Markov Process (SMP) formulation of composite services with failures and restarts. By explicitly including failure states into the SMP representation of a service, we can compute both its performance and reliability using a single SMP. We can also detect its performance and reliability bottlenecks by applying the formal sensitivity analysis technique. We demonstrate our approach by choosing a representative example that is validated using experiments on real web services.