This article proposes the application of techniques from knowledge engineering to the development of graphic interfaces. The current paradigm of knowledge-based systems is rooted in features such as declarative representation of knowledge, design modularity, and independence between data, knowledge, and control. The main advantage of this approach with respect to conventional programming techniques is that the incremental development of interfaces, as well as their modification and maintenance, is made easier. We present a human-machine interaction technique that seeks a compromise between simplicity and expressive power.