Principled design of visual languages for interaction

This paper reports on the Pictorial Computing Laboratory methodology for interactive visual systems (IVS) design, clarifying and deepening, in a systematic way the links between the theoretical aspects of the PCL research, and the results of experimental IVS design. The methodology is aimed at satisfying three principles: the user must always understand the effects of the system activity with respect to the execution of his/her task; the user must always be in control of the interactive computation, avoiding getting lost in the virtual space; and the system has to trap users´ errors and maintain itself viable, i.e. in a predictable set of states. To satisfy these principles, the IVS design is accomplished through different steps, each step producing a new visual language to be verified and validated