Towards QoS prediction based on composition structure analysis and probabilistic environment models

Complex software systems are usually built by composing numerous components, including external services. The quality of service (QoS) is essential for determining the usability of such systems, and depends both on the structure of the composition and on the QoS of its components. Since the QoS of each component is usually determined with uncertainty and varies from one invocation to another, the composite system also exhibits stochastic QoS behavior. We propose an approach for computing probability distributions of the composite system QoS attributes based on known probability distributions of the component QoS attributes and the composition structure. The approach is experimentally evaluated using a prototype analyzer tool and a real-world service-based example, by comparing the predicted probability distributions for the composition QoS with the actual distribution of QoS values from repeated actual executions.