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State Decomposition

Every state (or chart) has a decomposition that dictates what type of substates the state (or chart) can contain. All substates of a superstate must be of the same type as the superstate decomposition. State decomposition can be exclusive (OR) or parallel (AND).

Exclusive (OR) State Decomposition

Substates with solid borders indicate exclusive (OR) state decomposition. Use this decomposition to describe operating modes that are mutually exclusive. When a state has exclusive (OR) decomposition, only one substate can be active at a time.

In the following example, either state A or state B can be active. If state A is active, either state A1 or state A2 can be active at a given time.

Parallel (AND) State Decomposition

Substates with dashed borders indicate parallel (AND) decomposition. Use this decomposition to describe concurrent operating modes. When a state has parallel (AND) decomposition, all substates are active at the same time.

In the following example, when state A is active, A1 and A2 are both active at the same time.

The activity within parallel states is essentially independent, as demonstrated in the following example.

In the following example, when state A becomes active, both states B and C become active at the same time. When state C becomes active, either state C1 or state C2 can be active.