%0 Journal Article
%@ 1567-8326
%A Buscemi, Maria Grazia
%A Montanari, Ugo
%D 2011
%F eprints:114
%I Elsevier
%J Journal of Logic and Algebraic Programming
%K Process calculi; Service oriented computing; Constraint-based models
%N 1
%P 13-24
%T QoS Negotiation in Service Composition
%U http://eprints.imtlucca.it/114/
%V 80
%X 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 cj:πj in a choice is enabled if the constraint cj is entailed by the store of constraints and the prefix πj can be consumed. Moreover, the j-th branch can be selected not only if the corresponding guard cj:πj is enabled but also if cj is weaker than the constraints ci 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 strictly less expressive than ours.
%Z Copyright © 2010 Elsevier Inc. All rights reserved.   The 2nd Workshop on Formal Languages and Analysis of Contract-Oriented Software (FLACOS’08)