A Prototype for continuation-passing orchestration of composite web services

Abstract

Web services enable businesses to deliver services via the Web. In addition, Web services can be used to improve business efficiency, because Web services can often replace manual activities in a business process. A Web service can be composed of other simpler Web services using the abstraction traditionally known as workflows. The process of controlling the correct and reliable execution of a workflow is known as workflow enactment, but it can also be referred to as Web services orchestration. A centralized approach to Web services orchestration is not an optimal solution, when considering the decentralized nature of Web services and the Internet. The problem is that a centralized workflow engine can easily become a communication and processing bottleneck as well as a central point of failure. Therefore, a decentralized approach to Web services orchestration is needed in order to overcome these obstacles. However, some decentralized approaches require static analysis of workflow specifications, which implies that resources must be allocated prior to the workflow execution. As a result, resources are wasted. In this thesis a prototype is developed to demonstrate a decentralized Web services orchestration based on continuation-passing enactment of distributed workflows. This decentralized approach does not require any pre-allocation of resources, nor is it subject to the limitations of a centralized approach. The continuation-passing mechanism involves continuations, or the reminder of the executions, which are passed along asynchronous messages for workflow enactment.