Breaking Down Usability

Good usability of a system is the main goal of interface designers. Determining the usability is usually done afterwards by performing usability tests with users or by going through checklists. On the other hand, design guidelines and design heuristics give the designer assistance in improving the usability while designing. In practice the available checklists, tests, guidelines etc. differ in terms of structure, content and terminology and the suggestion is given that one list is more useful than another. This paper breaks down the concept of usability into a layered model that allows comparisons of the available lists and provides better understanding of them. The model also gives a framework for evaluation by showing which usability aspects can be tested empirically and what can be formally checked by analyzing designs during the design process itself.