4.2.8 Enter/Exit Actions

Enter actions of a state are written under the ENTER descriptor. Exit actions are written under the EXIT descriptor. There are two obligatory properties and one optional property for enter actions and exit actions:

• The N (source state) property or the S (new state) property specifies the state of those actions. For enter actions, since they are executed when a state is entered, the N property is used to identify the state. Conversely, for exit actions, since they are executed when a state is exited, the S property is used.

• The O (output) property specifies the actions to be executed. If there are multiple actions, they are written on consecutive lines and left aligned.

• The C (condition) property specifies the guard to be satisfied. It is similar to the C property of a transition. The guard is evaluated when the state is entered/exited.

  There may be multiple parts of enter/exit actions defined for a single state. This is done with multiple ENTER or EXIT descriptors with the same N or S property. The guards of those parts are mutually independent. Each guard only controls the execution of the actions under one descriptor.

Table 4.9: An example of the textual representation of an enter action and an exit action

The model with an enter action and an exit action in Figure 4.11 is translated into the textual representation in Table 4.9.