Software Design 2e - DIM

197The role of strategy in methodsFigure 9.3Contrasting transformation and elaboration design steps.These models were largely chosen because they are convenient forms for aiding theanalysis of the procedural aspects of design methods. Although we do not have scopein this book to utilise more detailed models of the actual procedural steps, the abilityto describe these can be useful when we need to review particular processes. As anexample of such a more detailed process model, that developed by Potts and Bruns(Potts and Bruns, 1988; Potts, 1989; Lee, 1991) does provide the means of performinga more detailed analysis of the factors involved in making individual design decisions,and an example of this is shown in Figure 9.4.Their model is based on the use of five entity types (the boxes) and eight binaryrelationships (the arcs). The relationships operate as follows (Potts, 1989).nnnnnnnnSteps modify artifacts. In ‘derivation’, a new artifact is created. In ‘revision’, a newversion of an existing artifact is created.Steps raise issues. This may occur automatically, but the issue may not have to beaddressed immediately.Issues review artifacts. An issue may be raised to review the property of an artifact.Positions respond to issues.Arguments support positions.Arguments object to positions. Arguments are often paired, with one supporting aposition and the other opposed to it.Arguments cite artifacts. The artifact provides evidence for the argument.Positions contribute to steps. A step is performed because a set of commitments hasbeen made.In Potts (1989) this model has been used to analyse the initial stages of the JSDmethod, and to model the processes involved. This form therefore provides a useful