This paper presents a methodology and a mix of conceptual models for addressing design and development of Web applications supported by rich interfaces. For specifying the high level design of the user tasks, we exploit business process models. In particular, we describe how to model the business process, transform it into data and navigation model of a Web application, and apply a presentation model for obtaining a Rich Internet Application (RIA). A standard business modeling language (BPMN) is used for describing workflows, which are then translated to a WebML specification of a Web application implemented according to the Single Page Paradigm, typical of RIAs. Finally, by integrating the RUX-Method features, refined Rich Interface design can be achieved.