Value Lifeline

d_ValueLifeline

Description

A Lifeline is the path an object takes across a measure of time, indicated by the x-axis. There are two sorts: Value Lifelines (defined here) and State Lifelines, both used in Timing diagrams.

A Value Lifeline shows the Lifeline's state across the diagram, with parallel lines indicating a steady state. A cross between the lines indicates a transition or change in state.

An example of a Value Lifeline is shown below:

TimingValueDiagram

See UML Superstructure Specification, v2.1.1, Figure 14.30, p. 520.

A Value Lifeline consists of a set of transition points. Each transition point can be defined with the following properties:

Property

Description

At time

Specifies the starting time for a change of state.

Transition to

Indicates the state to which the Lifeline is to change.

Event

Describes the occurring event.

Timing constraints

Refers to the time taken for a state to change within a Lifeline, or the time taken to transmit a message.

Timing observations

Provides information on the time of a state change or sent message.

Duration constraints

Pertains to a Lifeline's period at a particular state. The constraint could be instigated by a change of state within a Lifeline, or that Lifeline's receipt of a message.

Duration observations

Indicates the interval of a Lifeline at a particular state, begun from a change in state or message receipt.

In the example diagram above, the 10ms transition point has these properties:

Property

Text

At Time

10ms

Transition to

Waitcard

Event

Switch

Timing constraints

-

Timing observations

-

Duration constraints

d..3*d

Duration observations

-

Toolbox Icon

e_ValueLifeLine

Learn More:

OMG UML Specification

The OMG UML specification (UML Superstructure Specification, v2.1.1, p. 518) states:

Shows the value of the connectable element as a function of time. Value is explicitly denoted as text. Crossing reflects the event where the value changed.