Editing State diagram (section)

== Harel statechart ==
[[File:OO Modeling languages history.jpg|thumb|250px|Diagram showing how Harel's Statecharts contributed to object-oriented methods and notation]]
Harel statecharts,<ref name="Har87">[[David Harel]], [https://www.weizmann.ac.il/math/harel/sites/math.harel/files/users/user56/Statecharts.pdf Statecharts: A visual formalism for complex systems. Science of Computer Programming], 8(3):231–274, June 1987.</ref> invented by computer scientist [[David Harel]], are gaining widespread usage since a variant has become part of the [[Unified Modeling Language]] (UML).{{primary source inline|date=March 2018}} The diagram type allows the modeling of [[UML state machine#Hierarchically nested states|superstates]], [[UML state machine#Orthogonal regions|orthogonal regions]], and activities as part of a state.

Classic state diagrams require the creation of distinct nodes for every valid combination of parameters that define the state. For all but the simplest of systems, this can lead to a very large number of nodes and transitions between nodes ([[UML state machine#UML extensions to the traditional FSM formalism|state and transition explosion]]), which reduces the readability of the state diagram. With Harel statecharts it is possible to model multiple cross-functional state diagrams within the statechart. Each of these cross-functional state machines can transition internally without affecting the other state machines. The current state of each cross-functional state machine defines the state of the system. The Harel statechart is equivalent to a state diagram but improves its readability.