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State Lifeline
Description
A Lifeline is the path an object takes across a measure of time, as indicated by the x-axis. There are two sorts: State Lifelines (defined here) and Value Lifelines, both used in Timing diagrams.
A State Lifeline follows discrete transitions between States, which are defined along the y-axis of the timeline. Any transition has optional attributes of timing constraints, duration constraints and observations. An example of a State Lifeline is shown here:
Transition point properties
A State 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 changes. |
|
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 (for example, t..t+3). |
|
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 OK transition point has these properties:
Property |
Value |
|---|---|
|
At Time |
68 ms |
|
Transition to |
Idle |
|
Event |
OK |
|
Timing constraints |
t..t+3 |
|
Timing observations |
– |
|
Duration constraints |
– |
|
Duration observations |
– |
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Learn more
OMG UML Specification:
The OMG Unified Modeling Language specification, (v2.5.1, p.604) states:
This is the state of the classifier or attribute, or some testable condition, such as a discrete enumerable value.
It is also permissible to let the state-dimension be continuous as well as discrete. This is illustrative for scenarios where certain entities undergo continuous state changes, such as temperature or density