Analyzing the Usability of a Design Rationale Notation

Semiformal, argumentation-based notations are one of the main classes of formalism currently being used to represent design rationale (DR). However, our understanding of the demands on designers of using such representations has to date been drawn largely from informal and anecdotal evidence. One way to tackle the fundamental challenge of reducing DR’s representational overheads, is to understand the relationship between designing, and the idea structuring tasks introduced by a semiformal DR notation. Empirically based analyses of DR in use can therefore inform the design of the notations in order to turn the structuring effort to the designers’ advantage. This is the approach taken in this chapter, which examines how designers use a DR notation during design problem solving. Two empirical studies of DR-use are reported, in which designers used the QOC notation (MacLean et al., this volume) to express rationale for their designs. In the first study, a substantial and consistent body of evidence was gathered, describing the demands of the core representational tasks in using QOC, and the variety of strategies which designers adopt in externalising ideas. The second study suggests that an argumentation-based design model based around laying out discrete, competing Options is inappropriate during a depth-first, ‘evolutionary’ mode of working, centered around developing a single, complex Option. In addition, the data provide motivation for several extensions to the basic QOC notation. The chapter concludes by comparing the account of the QOC–design relationship which emerges from these studies, with reports of other DR approaches in use. 1. THE NEED FOR EMPIRICAL STUDIES OF DR IN USE 2. THE STUDIES: DESIGNERS, TRAINING, AND TASKS 3. CORE REPRESENTATIONAL TASKS IN QOC-AUTHORING 3.1. QOC authoring as an opportunistic activity 3.2. Classifying ideas 3.3. Naming and renaming 3.4. Structuring and restructuring 3.5. Summary 4. PROBLEMS USING QOC IN ‘EVOLUTIONARY’ DESIGN: TRYING TO ARGUE ABOUT ONE OPTION? 4.1. Difficulties encountered with QOC constructs Questions Options Criteria 4.2. Characterising the relationship between QOC and the two modes of designing 5. QOC’S EXPRESSIVENESS 5.1. Representing evolution within QOC structures 5.2. Expressing constraints and dependencies 5.3. The subtleties of expressing Options, Criteria, and Assessments 6. RELATIONSHIP TO REPORTS OF OTHER DR APPROACHES IN USE 7. CONCLUSIONS 8. REFERENCES