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Chapter to appear in ?Design Rationale: Concepts, Techniques and Use?

Moran T.P. and Carroll J.M. (Eds.), 1995, in press. Lawrence Erlbaum Associates: NJ

Analysing the Usability of a Design Rationale Notation

Simon Buckingham Shum

Human-Computer Interaction Group
Department of Psychology
University of York
York YO1 5DD
UK
sjbs1@york.ac.uk
tel: +44 1904-433165
fax: +44 1904-433181

ABSTRACT

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.