Web Services, Policies, and Context: Concepts and Solutions
Despite the extensive adoption of Web services by IT system developers, they still lack the capabilities that could enable them to match and eventually surpass the acceptance level of traditional integration middleware (e.g., CORBA, Java RMI). This lack o
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Zayed University, U.A.E., [email protected] The University of Adelaide, Australia, [email protected] Claude Bernard Lyon 1 University, France, [email protected] Louvain School of Management & University of Namur, Belgium, [email protected]
1 Introduction Despite the extensive adoption of Web services by IT system developers, they still lack the capabilities that could enable them to match and eventually surpass the acceptance level of traditional integration middleware (e.g., CORBA, Java RMI). This lack of capabilities is to a certain extent due to the triggerresponse interaction pattern that frames the exchanges of Web services with third parties. Adhering to this interaction pattern means that a Web service only performs the requests it receives without considering its internal execution state, or even questioning if it would be rewarded for performing these requests (e.g., to be favored over similar Web services during selection). There exist, however, several situations that insist on Web services self-management so that scalability, flexibility, and stability requirements are satisfied. The objective of this chapter is to discuss the value-added of integrating context and policies into a Web services composition approach. Web services offer new opportunities to deploy B2B applications, which tend to crosscut companies’ boundaries. Web services are independent from specific platforms and computing paradigms, and have the capacity to form high-level business processes referred to as composite Web services [3]. Policies are considered as external, dynamically modifiable rules and parameters that are used as input to a system [13]. This permits to the system to adjust to administrative decisions and changes in the execution environment. In the field of Web services, policies are intended to specify different aspects of the behavior of a Web service, so this one can align its capabilities to users’ requirements and resources’ constraints. Context “... is not simply the state of a predefined environment with a fixed set of interaction resources. It is part of a process of interacting with an ever-changing environment composed of reconfigurable, migratory, distributed, Z. Maamar et al.: Web Services, Policies, and Context: Concepts and Solutions, Studies in Computational Intelligence (SCI) 116, 39–55 (2008) c Springer-Verlag Berlin Heidelberg 2008 www.springerlink.com
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and multiscale resources” [4]. In the field of Web services, context is used to facilitate the development and deployment of flexible Web services. Flexibility refers to a Web service that selects appropriate operations based on the requirements of the business scenario that this Web service implements. While context and policies are separately used for different needs of Web services, this chapter discusses their role in framing the composition process of Web services. We propose a three-level approach to compose Web services. This approach does not only make Web services bind to each other, but emphasizes th
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