Modelling the relationship between state and display in interactive systems

Abstract

For many interactive systems, and in particular designs influenced by the direct manipulation style of interaction, the user’s ability to have immediate visual and manipulative access to all data is limited by the physical constraints of the display. A significant design concern therefore is the development of appropriate user models and complementary system models to support understanding of commands that are affected by these constraints. In this paper, the relationship between state and display is modelled mathematically to aid more precise understanding of the nature of direct manipulation as an interaction style, and the consequences of display boundary and other related limitations. Since it is unlikely that there is direct manipulative access to all data, we will distinguish between normal and exceptional models of interactive behaviour. Exception models describe the behaviour of the system when direct manipulation principles are transgressed.