Modelling status and event behaviour of interactive systems

Interactive systems involve both events which occur at specific moments (e.g. keystrokes, mouse clicks and beeps) and more persistent status phenomena which can be observed at any time (e.g. the position of the mouse, the image on the screen). Most formalisms used for interactive systems concentrate on one aspect or another, and may be asymmetric in their treatment of input and output. Notationsand models for interface specification are classified in the paper by the way they treat status and event phenomena in their input and output. This is used to construct a model and associated notation which incorporates both. By specifying examples using this model important design issues are highlighted which would be missed if either status or event phenomena were not properly treated.