Towards the principled design of software engineering diagrams

Diagrammatic specification, modelling and programming languages are increasingly prevalent in software engineering and, it is often claimed, provide natural representations which permit intuitive reasoning. A desirable goal of software engineering is the rigorous justification of such reasoning, yet many formal accounts of diagrammatic languages confuse or destroy any natural reading of the diagrams; hence they cannot be said to be intuitive. The answer, we feel, is to examine seriously the meaning and accuracy of the terms: "natural" and "intuitive" in this context. The paper highlights, and illustrates by means of examples taken from industrial practice, an ongoing research theme of the authors. We take a deeper and more cognitively informed consideration of diagrams which leads us to a more natural formal underpinning that permits: (i) the formal justification of informal intuitive arguments, without placing the onus of formality upon the engineer constructing the argument; and (ii) a principled approach to the identification of intuitive (and counter-intuitive) features of diagrammatic languages.