Elements of a detailed state model

The following shows a description of a detailed state model.

Figure 5.1: Example of a detailed state model

A state model includes: a set of events ($\Sigma$), a finite set of states (S), an initial state ($S0 \in S$) and a transition function (F).

• Events includes system operations (System concepts operations) and actors operations (Concepts operations).

  In addition to operations, events also include timeouts corresponding to Timers expiry. Timers are associated with states. They count the time elapsed while the system sits in a particular state.

• States describe situations in which the system and environment may be at some point in time.

  A State situation is defined as a set of characteristic conditions.

  A characteristic condition is either a condition (i.e. a valuation of a domain entity) or a timeout condition.

  Two states are identical if they have the same characteristic conditions.

  States in the example are listed with their set of characteristic conditions. As an example, state 4 characteristic conditions are {Card is inserted, Alarm is System Status, status is irregular, PMSystem is ON}.

  Notice that all domain entities always have a value that may be explicit or unknown, in a given state. As an example, since attribute Display of the PMSystem doesn't have an explicitly defined value in state 4, its implicit value is unknown value.

  A timeout condition reflects the 'relevancy' of the fact that a timer expired. As an example, timeout condition Timer0:20 second that characterizes state 5 means that timer Timer0 that was set for 20 seconds has expired, and that information is 'relevant'.

  A state $s_{b}$ is a sub-state of a state $s_{a}$ (its super-state), if its characteristic conditions include those of $s_{a}$ in the logical sense. As an example, state 1 in the state model is a super-state of state 2. State 2 characteristic conditions include state 1 characteristic conditions.

  A state may have more than one direct super-states. State 17 which direct super-states are states 9 and 16 is an example of such a state.

• A transition specifies the change from a state (a starting situation) to another state (a resulting situation).

  A transition includes:

  • a starting state; the situation before the transition,
  • an event that makes the transition happen, and
  • a resulting state; the new situation after the system operationransition.
  As an example 5---[eject card]-->6 describes a transition from state 5 to 6 on event eject card.

  Any transition starting from a state s also applies to all the sub-states of s. As an example transition 1---[press cancel button]-->23 from state 1 applies to all sub-states of state 1 (all the other states in the state model).

• A state model initial state represents the initial situation of the system and environment before any transition has been fired.