Recording the reasons for design decisions

We outline a generic model for representing design deliberation and the relation between deliberation and the generation of method-specific artifacts. A design history is regarded as a network consisting of artifacts and deliberation nodes. Artifacts represent specifications or design documents. Deliberation nodes represent issues, alternatives or justifications. Existing artifacts give rise to issues about the evolving design, an alternative is one of several positions that respond to the issue (perhaps calling for the creation or modification of an artifact), and a justification is a statement giving the reasons for and against the related alternative. The model is applied to the development of a text formatter. The example necessitates some tailoring of the generic model to the method adopted in the development, Liskov and Guttag's design method. We discuss the experiment and the method-specific extensions. The example development has been represented in hypertext and as a Prolog database, the two representations being shown to complement each other. We conclude with a discussion of the relation between this model and other work, and the implications for tool support and methods.