Abstract
An approach to the specification of a Virtual Reality (VR) interactive environment is presented, which merges and generalizes two methods recently proposed in the literature: the PCL characteristic pattern approach to WIMP system design and the Interaction Locus approach to interactive navigation in 3-D virtual spaces. The merging of the two points of view allows the refinement of the model of interaction of a user with a virtual environment and leads to the definition of "real" and "virtual" characteristic pattern, which the discussion shows to be an important concept for the designer to properly undertake the design of complex virtual reality systems.