Lifelines

In Unified Modeling Language (UML) sequence diagrams, a lifeline represents a connectable element of the enclosing classifier, including inherited properties or parameters, and describes how each instance participates in the interaction over a period of time. Each instance in an interaction is represented by a lifeline.

As the following figure illustrates, a lifeline consists of a name in a rectangle, which is called the head, on top of a vertical dashed line, which is called the stem, in an interaction frame.

The head of the lifeline is displayed as a rectangle, with the stem of the lifeline displayed as a vertical dashed line that connects to the center bottom of the rectangle.

The instance name and type appears in the head of the lifeline. The stem represents the instance that the lifeline represents. Messages, which are sent and received by the instance, appear on the lifeline in a chronological order.

Parent topic: Sequence diagrams and diagram elements

Related concepts
Sequence diagrams
Interaction frames
Messages
Execution occurrences
Interaction occurrences
Combined fragments
Interaction operators
Interaction operands
Guard conditions
Stop nodes

Related tasks
Developing lifelines
Adding create or destroy messages to lifelines

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