State machine-related constructs are described below.
StateMachine
The purpose of a state machine is to model event-driven execution behavior across the computing continuum by enabling transitions between states or by accommodating nested state machines that are executed concurrently.
Nested state machines allow a state machine to express concurrent behavior while providing mechanisms to observe and influence the execution of the parent state machine. They begin execution simultaneously with the parent state machine.
A state machine consists of one or more states, which are reached through state transitions. At any given moment, only one state within a state machine is active, while all other states remain inactive.
As with collaborative state machines, local and persistent data can be declared within a state machine.
new StateMachine {
name = "SM2"
states {
new State {...}...
}
stateMachines {
new StateMachine {...}...
}
localData = new Data {...}
persistentData = new Data {...}
}
Listing 7: A StateMachine construct.
The following keywords can/must be provided:
| Keyword | Description | Type | Optional |
|---|---|---|---|
| name | Name of the state machine. | string | No |
| states | Collection of states. | list of State | No |
| stateMachines | Collection of state machines. | list of StateMachine | No |
| localData | Local data. | Data | Yes |
| persistentData | Persistent data. | Data | Yes |
name
The name keyword specifies the name of the state machine and may be used for diagnostic purposes or referencing.
The name of a state machine is not referenced inside a description.
The validity of a name is implementation-specific.
states
The states keyword is used to specify the collection of atomic states included in the state machine.
Atomic states are described using the State construct.
At least one state must be declared.
State.names must be unique.
Exactly one initial state must be declared.
Initial states must not have inward transitions.
Terminal states must not have outward transitions.
Every state must be reachable (it must have a transition leading into it, or it must be the initial state).
stateMachines
The stateMachines keyword is used to specify the collection of nested state machines.
Nested state machines are described using the StateMachine construct.
localData / persistentData
The localData and persistentData keywords allow for lexically declaring respectively the local and persistent data at the state machine level.
Data described at the state machine level is accessible from the state machine and any component hierarchically below it, see dynamic extent.