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Value Lifeline
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.
This is an example of a Value Lifeline:
See UML Superstructure Specification, v2.1.1, Figure 14.30, p.520.
Transition point properties
A Value Lifeline consists of a set of transition points. Each transition point can be defined with these 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. |
Example properties
In the example diagram, 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 |
– |
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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.