Workflow-based composition of Web-services: a business model or a programming paradigm?

While SOAP/XML is perceived as the appropriate interoperability level for Web-services, companies compete to provide workflow-based tools for Web-service integration. This paper presents the design and implementation of a prototype workflow management system for building new Web-services from a workflow of existing Web-services. This enables the creation of multiple layers of value-added service providers and provides fast service creation, customisation and deployment. The system caters for multiple workflow paradigms, provides an extensible language for workflow specification and emphasises encapsulation and tight constraints on workflow execution. To expose a workflow of Web-services as a Web-service, several design steps have been required including the deployment as a Web-service of the generic workflow engine and a generalisation of the Visitor Pattern to concurrent visitors.