Communication Priorities and Stochastic Measures for Web Services Modeling

Service Oriented Architecture is an important trend in the development of services composed of loosely coupled, heterogeneous and interacting components. We first consider COWS, which is a language tailored to model the behavioural aspects of these systems. We analyse the peculiarities of the communication mechanism of the language, a key ingredient in its modelling capabilities, presenting a separation result between a fragment of CCS equipped with global priorities and the fragment of COWS relevant for its communication mechanism. We then consider a stochastic approach to model the quantitative aspects of Web Services through SCOWS, a stochastic extension of COWS. We present a prototype tool, named SCOWS_LTS, for the derivation of the complete representation of the behaviour of a SCOWS model as a Continuous Time Markov Chain. In order to validate the approach, a number of case studies are modelled in SCOWS considering both the SOA and the concurrency literature. Using PRISM as model checker, the results of the simulation phase are analysed using properties written to check the probabilistic behaviours of the considered systems.