State machine

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 Context {...}
  persistentData = new Context {...}
}

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.	Context	Yes
persistentData	Persistent data.	Context	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.

Info

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.

Rule

At least one state must be declared.

Rule

State.names must be unique.

Rule

Exactly one initial state must be declared.

Rule

Initial states must not have inward transitions.

Rule

Terminal states must not have outward transitions.

Rule

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.