The success of service-oriented computing has important implications on how people develop user interfaces. This paper discusses a method for supporting the development of interactive applications based on the access to services, which can be associated with user interface annotations. In particular, we show how model-based descriptions can be useful for this purpose and the design of an authoring environment for the development of interactive front-ends of applications based on Web services. A prototype of the authoring environment is presented. Categories and Subject Descriptors H5.m. Information interfaces and presentation (e.g., HCI). General Terms Design, Human Factors, Languages Keywords User Interface Composition, Model-based Design, Web services.