State Diagram

A state diagram describes the behavior of systems by a finite number of states with corresponding transitions.

Diagram Model

Name	Graphical Representation	Description
Pseudo States		Entry and exit points are used to start and stop the state machine. The termination point is used for abnormal exiting.
State		A simple state defines a situation where certain well-defined conditions are valid. The current state of an object is called active state.
State Activities		Entry, do and exit activities can be specified within the state element.
Transition		A transition is a directed relationship that describes a change from source state to target state (which can be the same state). A transition is triggered by events: call event: request to execute an operation signal event: asynchronous signal received change event: one or more attribute values of the object changed time event: point in time reached or time passed any receive: any event where the reaction is not specified by other transitions Events can be ignored, can trigger a state change or can trigger state internal actions without state change.
Sub-State Machine		This element specifies a state which is detailed in another diagram.
Composite State		Also defines a sub-state machine, but the internal states are modelled directly in the same diagram. A composite state can have own entry and exit points or the internal states are directly connected to the other states.
Decision		Usually a decision is modelled by different transitions from one state to other states. But in some cases a decision can make a diagram more readable and reduce complexity.
Fork and Join		This can be used to model parallel states in different threads, cores, etc.

Example