## 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.

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