A Practical Way for Projects to Visualize Design Rationale

Design rationale remains poorly explained and rarely modelled on projects in industry. However, the reasons for design decisions are important when a specification has to be re-examined, eg for reuse, for safety, for validation, or to satisfy stakeholders that a project is justified. A practical notation must be extremely simple but expressive, given industry´s reluctance. This paper illustrates how a minimal box-and-arrow notation is sufficient for modelling Toulmin argumentation, and helpful on transportation projects. These critically depend on properly documented rationale as they are subject to public inquiry. The use of Dewar signposts to connect such rationale models to changing events in the world is illustrated.