Service-Oriented Workflow: The DySCo Framework

From a business perspective, Web services represent a new channel for the offer as well as the acquisition of business capabilities. The full automation of the interaction process between providers and consumers is a peculiarity of the Web service channel. Beyond electronic data transfer, automation extends to all aspects of business interaction. The negotiation of terms and conditions for service delivery and the management of service-level agreements are just some examples. Since their early definition, composition has been a central concept for Web services. In the Web service model, the provider of a new Web service WS drives the composition of internal and external capabilities in order to produce a new capability. Both internal and external capabilities are modelled as Web services that act as components for WS. Similarly, WS can be used as component for other Web services. The fact that a capability is available internally or needs to be acquired externally reflects on the business as well as technical design of the service. The Web service model enforces the separation between a service component and the related service provider. Different providers can be selected for the same capability under different circumstances. From a business as well as a technology perspective, Web services enable dynamic integration for service providers. The explicit management of the interaction processes associated to the delivery of a service is a fundamental aspect of Web services. INTERACTION PROCESSES The decupling of service logic and service provider is closely related to the most noticeable feature of the Web service model: processoriented interfaces. In traditional component models, function signatures often represent the only information on the interaction requirements of a component. While the invocation of a function can trigger complex interaction processes, interaction logic is not formally exposed. In the Web service model, the interaction processes associated to a Web service are explicitly formalized and exposed. WSCL (Web Service Choreography Interface) and BPEL4WS (Business Process Execution Language for Web Services) are examples of languages for the formalization of interaction processes associated to Web services. An immediate benefit of process-oriented interfaces is that they open new possibilities for static as well as dynamic composition of services. As an example, the interaction protocols between individual Web services can be automatically negotiated and adapted. Workflow provides an established framework for handling the interaction processes of individual Web services, as well as the orchestration of needs intrinsic in business solutions based on the composition of multiple Web services.