Web service technologies are best exploited by composing services, and BPEL (Web Services Business Process Execution Language) is adopted industrial-wide as the de facto service composition standard. However, a BPEL composite service is typically treated as a fully automated service flow that orchestrates multiple web services and involves no user interactions - a desirable feature for service delivery, and is presently not included in the BPEL standard. In this work, we propose an extension to BPEL to infuse user interactions into composite services along three dimensions: (1) to develop two BPEL extension activities to describe the inner workings of user interactions in BPEL service and the rendering of service user interfaces; (2) to provide a wizard-style mechanism to guide the user to interact with the service flow in accordance with the sequence of service execution; and (3) to devise a UI service communication protocol to facilitate secure cross-domain communication among UI services from various domains. An enhanced BPEL engine with a service UI rendering engine has been accordingly developed.
