Formalising an Understanding of User-System Misfits

Many of the difficulties users experience when working with interactive systems arise from misfits between the user’s conceptualisation of the domain and device with which they are working and the conceptualisation implemented within those systems. We report an analytical technique called CASSM (Concept-based Analysis for Surface and Structural Misfits) in which such misfits can be formally represented to assist in understanding, describing and reasoning about them. CASSM draws on the framework of Cognitive Dimensions (CDs) in which many types of misfit were classified and presented descriptively, with illustrative examples. CASSM allows precise definitions of many of the CDs, expressed in terms of entities, attributes, actions and relationships. These definitions have been implemented in Cassata, a tool for automated analysis of misfits, which we introduce and describe in some detail.