Dynamic Substitutability Analysis of Web Service Composition via Extended Pi-Calculus

Web service composition often fails due to the exceptions of some member service and dynamic substitutability of Web service composition refers to the ability of using candidate services to replace those malfunction services in order to improve the robustness and dependability of Web service composition. In this paper, we introduce the notions of signal process and event process structure into polyadic pi-calculus and present their syntactic descriptions, operational semantics and structural congruence relationships. After that, we also discuss the behavioral equivalence and substitutability conditions of Web services based on bisimulation theory of pi-calculus and give a case study to demonstrate how to use our extended pi-calculus to describe the dynamic substitutability of Web service composition and the dynamic evolution of system structure due to the substitution from a global view by taking candidate services into consideration.