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Sensoria Bibliography Site QoS Negotiation in Service Composition
Maria Grazia Buscemi, Ugo Montanari
abstract:
Service composition in Service Oriented Computing concerns not only integration of heterogeneous distributed applications but also dynamic selection of services. Quality of Service (QoS) plays a key role in service composition as services providing the same functionalities can be differentiated according to their QoS guarantees. At subscription time, a service requester and a provider may sign a contract recording the QoS of the supplied service. The cc-pi calculus has been introduced as a constraint-based model of QoS contracts. In this work we propose a variant of the cc-pi calculus in which the alternatives in a choice rather than being selected non-deterministically have a dynamic priority. Basically, a guard $c_j:\pi_j$ in a choice is enabled if the constraint $c_j$ is entailed by the store of constraints and the prefix $\pi_j$ can be consumed. Moreover, the $j$-th branch can be selected not only if the corresponding guard $c_j:\pi_j$ is enabled but also if $c_j$ is weaker than the constraints $c_i$ of the other enabled alternatives. We prove that our choice operator is more general than a choice operator with static priority. Finally, we exploit some examples to show that our prioritised calculus allows arbitrarily complex QoS negotiations and that a static form of priority is stricly less expressive than ours.
