6.1 Diagrams – Why?

6.1.1 Introduction

Why do we use diagrams? Not 'why do we use software diagrams?', but why do we use diagrams at all? We couldn't imagine civil, mechanical, or electrical engineers working without diagrams. And, at a much simpler level, try putting together self-assembly furniture using only written instructions (no pictures).

This takes us into the area of psychology. Our experiences show us that pictures must convey information in a different way from words, and in a way that is clearer and easier to understand. T. R. G. Green [GRE82] describes this in terms of temporal processes, dealing with many aspects of the problem, including:

• Recognition – is the process familiar?
• Modularity – what chunks can the description be broken into?
• Tractability – how can a modification be made?
• Sequence – in what order do the events happen?
• Circumstance – if such and such happens, what does...