statechartsgraphs

Statecharts graphs, or statecharts, are graphical representations used to model the behavior of reactive systems. They extend traditional finite state machines by incorporating hierarchical states, concurrent regions, and explicit event-driven transitions, enabling compact descriptions of complex software and hardware behavior.

Originating with David Harel in 1987, statecharts were designed to address the inadequacies of flat state machines for large systems. They describe states as nodes and transitions as labeled edges, but allow states to contain nested substates and parallel regions, which can be activated simultaneously.

Key features include hierarchy (superstates and substates), concurrency (AND-state composition with parallel regions), and history mechanisms (deep or shallow) to remember the last active substate. Transitions may have events, guards, and actions, and entry and exit actions can be attached to states.

Graphically, a statechart is a directed, labeled graph with composite states supported by hierarchical structure; the semantics define how an automaton reaches configurations and processes events. Statecharts can be used to model requirements, design interactions, and guide development in real-time and embedded systems. They help manage state explosion through hierarchical decomposition and clear separation of concerns.

Applications of statecharts graphs span user interfaces, control systems, aerospace, automotive, and robotics. Tools and standards reflect their influence: UML 2.0 includes state machine diagrams inspired by statecharts, and many modeling environments provide editors, simulation capabilities, and code generation for statechart-based models.

See also: finite state machine, UML state machine diagram, Mealy machine, Harel statecharts, Petri nets.