Abstract
The VR-DIS system is a design application for the Building and Construction industry (VR-DIS stands for Virtual Reality - Design Information System). The user interface is characterised by a mixed representation of the task domain. A pictorial representation of the appearance of the building is combined with a visualisation of the formal description of the design. The latter visualisation is worked out as a highly interactive 3D graph in which relation types are mapped on distinct planar directions and the browsing history is visualised in the third dimension. We discuss the theoretical foundations of the interface as a whole and those of the developed 3D graph.