ABSTRACT
Semiformal, argumentation-based notations are one of the main classes of formalism currently being used to represent design rationale (DR). However, using them makes particular demands on the designer, which cannot be ignored by proponents of such approaches. One way to tackle the challenge posed by DR's representational overheads is to understand the relationship between designing, and the idea-structuring tasks introduced by the DR notation. This can then inform the design of the notation in order to support the process of externalizing ideas within the notational vocabulary, and turn the structuring effort to the designers' advantage. Whereas our understanding of the demands on designers of using such representations has to date been drawn largely from informal and anecdotal evidence, in recent years, studies have demonstrated that the close study and characterization of design activity "in the natural" is a powerful way to define requirements for subsequent support technology. It is within this paradigm that the current work has been conducted. Two studies of DR in use are reported, in which designers used the QOC (Questions, Options, and Criteria) notation (MacLean, Young, Bellotti, & Moran, 1991 [chapter 3 in this book]) 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 that designers adopt in externalizing ideas. The second study suggests that an argumen tation-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 understanding of QOC that emerges from these studies, with reports of other argumentation-based approaches in use.
