Iteration in design processes

Ideally, specifications for all products should be based on a systematic analysis of what prospective users need to do, and how they can do it most effectively and efficiently. In practice, the design process is disturbed by many 'pragmatic' factors, such as conflicting constraints, interference from management, personnel changes in design teams and technological progress leading to new possibilities. Therefore, design is an iterative process. In this paper the design task of training simulator specification is used to illustrate the iterative nature of design processes. The results of two empirical studies show no clear relation between the amount of iteration and the quality of the resulting designs. Frequent iteration can be part of both an effective and an ineffective design style. In order to develop support for managing iteration during the design process it is necessary to understand in which circumstances iteration needs to occur, and how these circumstances can be predicted or recognised. For this purpose, a list of triggers for iteration is described. Finally, a number of measures to help designers to manage an iterative design process is proposed