Misleading Behaviour in Interactive Systems

We introduce the idea of partial behaviours in user interfaces. A partial behaviour can beguile users, and may be a cause of interaction problems — however, it is possible to identify and remove them early in the design process, making them a useful concept for interaction design. A characterisation of partial behaviours is presented, in terms of a matrix algebra model of interactive systems. We use the model to show some real interfaces have undesirable and apparently unnecessary partial behaviours, and we discuss how choices made when modelling affect our notion of partiality. We also briefly describe a design tool that provides automatic support for partial behaviour analysis.