UML State Diagram

The Unified Modeling Language (UML) state diagram is essentially a Harel statechart with standardized notation, which can describe many systems, from computer programs to business processes. The following are the basic notational elements that can be used to make up a diagram:

• Filled circle, pointing to the initial state;

• Hollow circle containing a smaller filled circle, indicating the final state (if any);

• Rounded rectangle, denoting a state. Top of the rectangle contains a name of the state. Can contain a horizontal line in the middle, below which the activities that are done in that state are indicated

• Arrow, denoting transition. The name of the event (if any) causing this transition labels the arrow body. A guardAccording to Pilone, the only predefined guard condition is ELSE. No other examples are provided within that publication. expression may be added before a "/" and enclosed in square-brackets ( eventName[guardExpression] ), denoting that this expression must be true for the transition to take place. If an action is performed during this transition, it is added to the label following a "/" (eventName[guardExpression]/action ).

• Thick horizontal line with either x>1 lines entering and 1 line leaving or 1 line entering and x>1 lines leaving. These denote join/fork, respectively.

Example UML state diagram