Timing Diagrams

Timing diagrams are UML interaction diagrams used to show interactions when a primary purpose of the diagram is to reason about time. Timing diagrams focus on conditions changing within and among lifelines along a linear time axis. Timing diagrams describe behavior of both individual classifiers and interactions of classifiers, focusing attention on time of events causing changes in the modeled conditions of the lifelines.

The following nodes and edges are typically drawn in a UML timing diagram: lifeline, state or condition timeline, destruction event, duration constraint, time constraint.

You can find some timing diagram examples here:

Lifeline

Lifeline is a named element which represents an individual participant in the interaction. While parts and structural features may have multiplicity greater than 1, lifelines represent only one interacting entity. See lifeline from sequence diagrams for details.

Lifeline on the timing diagrams is represented by the name of classifier or the instance it represents. It could be placed inside diagram frame or a "swimlane".

Lifelines representing instances of System and Virus.

Lifelines representing instances of System and Virus

State or Condition Timeline

Timing diagram could show states of the participating classifier or attribute, or some testable conditions, such as a discrete or enumerable value of an attribute.

Timing diagram could show discrete states or conditions of participants.

Timeline shows Virus changing its state between Dormant, Propagation, Triggering and Execution state

UML also allows the state/condition dimension be continuous. It could be used in scenarios where entities undergo continuous state changes, such as temperature or density.

Duration Constraint

Duration constraint is an interval constraint that refers to a duration interval. The duration interval is duration used to determine whether the constraint is satisfied.

The semantics of a duration constraint is inherited from constraints. If constraints are violated, traces become negative which means that system is considered as failed.

Duration constraint is shown as some graphical association between a duration interval and the constructs that it constrains.

Duration constraint example - ice should melt into water in 1 to 6 minutes.

Ice should melt into water in 1 to 6 minutes

Time Constraint

Time constraint is an interval constraint that refers to a time interval. The time interval is time expression used to determine whether the constraint is satisfied.

The semantics of a time constraint is inherited from constraints. All traces where the constraints are violated are negative traces, i.e., if they occur, the system is considered as failed.

Time constraint is shown as graphical association between a time interval and the construct that it constrains. Typically this graphical association is a small line, e.g., between an occurrence specification and a time interval.

Time constraint example - Person should wake up between 5:40 am and 6 am.

Person should wake up between 5:40 am and 6 am

Destruction Occurrence

Destruction occurrence is a message occurrence which represents the destruction of the instance described by the lifeline. It may result in the subsequent destruction of other objects that this object owns by composition. No other occurrence may appear after the destruction event on a given lifeline.

Complete UML name of the occurrence is destruction occurrence specification. Until UML 2.4 it was called destruction event, and earlier - stop.

The destruction event is depicted by a cross in the form of an X at the end of a timeline.

Account lifeline is terminated.

Virus lifeline is terminated

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