This paper is concerned with the development and clarification of a generic framework for assessing the effectiveness of users interfaces with respect to user tasks. Informal cognitive dimensions have been put forward as key characterisations of interaction and information structures which focus upon factors central to successful use. In addition, suggested dependencies between dimensions cannot be analysed without clearer definitions being adopted. Our present investigation focuses upon four cognitive dimensions, and develops a system based account of interaction used to interpret the dimensions. Secondary notation refers to the presence of notational flexibility that is independent of a notation's intended semantics.
Viscosity is a measure of resistance to local change.
For interactive systems this refers to the complex activities that minor modifications and manipulations can entail. Hence, a conceptually simple modification becomes a complex activity. Knock-on viscosity concerns the manner in which a system environment can often limit or restrict how a goal is reached. With examples of knock-on viscosity, when a primary goal is achieved, the system negates other properties still required by the user. We model knock-on viscosity by characterising how achieving some goals can interfere with, or disrupt, others.