Causality

Simple history systems such as Undo and Redo permit retrieval of earlier or later interaction states, but advanced systems allow powerful capabilities to reuse or reapply combinations of commands, states, or data across interaction contexts. Whether simple or powerful, designing interaction history mechanisms is challenging. We begin by reviewing existing history systems and models, observing a lack of tools to assist designers and researchers in specifying, contemplating, combining, and communicating the behaviour of history systems. To resolve this problem, we present CAUSALITY, a conceptual model of interaction history that clarifies the possibilities for temporal interactions. The model includes components for the work artifact (such as the text and formatting of a Word document), the system context (such as the settings and parameters of the user interface), the linear timeline (the commands executed in real time), and the branching chronology (a structure of executed commands and their impact on the artifact and/or context, which may be navigable by the user). We then describe and exemplify how this model can be used to encapsulate existing user interfaces and reveal limitations in their behaviour, and we also show in a conceptual evaluation how the model stimulates the design of new and innovative opportunities for interacting in time.