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Over the last few years we have been developing a perspective on design which emphasises the role and representation of design rationale (eg MacLean et al., 1989; MacLean et al., 1991b). We refer to the approach as Design Space Analysis (DSA). One of its key characteristics is that the output of design is conceived of as a design space rather than a single artifact. The approach therefore contrasts with the traditional conception of design which assumes that the eventual output is simply a specification or artifact. The final artifact, although embodying the designer's decisions, does not normally preserve any of the thinking and reasoning that went into its creation. We use a semi-formal notation (called QOC, for Questions, Options & Criteria) to represent the design space around an artifact being produced. This design space is an explicit representation of alternative design options and reasons for choosing among those options. The main concepts we use for the representation are Questions which highlight key issues in the design, Options which are effectively answers to the Questions and Criteria which are the reasons that argue for or against the possible Options.

DSA is a central part of a long term project in which we are addressing a wide range of issues in the software life cycle from early design through to maintenance and re-design. An important set of properties we are exploring relate to the support of group processes in design. Explicit documentation of the rationale involved in the design promises to be a useful aid for communication between members of the design team, between designers and users and between the current design …