RaBBiT (Requirements Building for Building Types) provides computational support for architectural programming or requirements modeling in building design. A highly interactive graphical user interface (GUI) allows users to adapt RaBBiT to various programming styles and terminologies. Since users are not expected to have any prior computer programming experience, the design of RaBBiT’s GUI posed particular challenges, which we attempted to meet through a direct-manipulation interface based on the model-world metaphor.