In addition to UML and
SysML, these charts are used in other languages too.
3.8.2 Lifeline
3.8 Interaction Diagrams
Defi nition
A lifeline represents a communication partner in an interaction. It describes
the name, the type, and the lifecycle of the element.
A communication partner represented by a lifeline is a role. The same model element
is also used in composite structure diagrams??”the internal block diagram
in SysML. This diagram shows who the role is connected with (i.e., with whom
it can communicate). Here in the sequence diagram we can describe the actual
communication.
The header of a lifeline is denoted similarly to the pertaining element from the
composition structure diagram. If you are familiar with the sequence diagrams of
UML 1 you will probably notice that the name of the lifeline is no longer underlined.
The underscore is the notation for objects, and communication partners in
UML 1 sequence diagrams are objects. In UML 2??”and thus in SysML too??”they are
roles rather than objects. This is a minor formal difference that shouldn ??™ t irritate you
in practice.
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