Probabilistic Quality of Service aware Service Selection

In software-as-a-service paradigms software systems are no longer monolithic pieces of code executing within the boundaries of an organisation, on the contrary, they are conceived as a dynamically changing collection of services, collectively executing, in pursuit of a common business goal. An essential aspect of service selection is determining whether the Quality of Service (QoS) profile of a service satisfies the QoS requirements of a client. In realistic execution environments, such QoS values might be influenced by external, non-controllable events, making it impossible for the service provider to guarantee that the values characterised by a QoS profile will be met, naturally leading to the need of a probabilistic interpretation of QoS profile. In this work we propose: 1) a model for describing probabilistic QoS profiles based on multivariate continuous probability distributions, 2) a language for describing probabilistic QoS requirements, and 3) an automatic procedure for assessing whether a probabilistic QoS profile satisfies a probabilistic QoS requirement.