Diagrammatic reasoning with statecharts: a cognitive approach for software/systems engineers

The behavior of reactive systems can be rigorously specified and verified via mathematical notation, such as temporal logic. However, for all but the simplest models, it is difficult for the reader to understand the intent of the model, and, for that matter, may be difficult for the model designer to accurately specify the desired behavior. Visual or "iconic" models have addressed this difficulty. Modeling tools typically include a mock-user interface builder and a graphical behavioral specifier, typically in the form of a Statechart editor (typical examples of such tools are Mathworks, Rapid, Statemate and Rhapsody). Statecharts solved the problem of combinatorial state explosion via encapsulation of OR and AND states. However, in order to minimize the corresponding transition explosion, Statecharts freely use global (i.e., global with respect to the Statechart) events and transitions that transcend state hierarchical boundaries. The paradoxical utilization and violation of encapsulation makes it difficult to apprehend the intent of even relatively simple Statecharts. We expound a pattern-based cognitive approach to this problem.