The elements of an interaction are essentially lifelines and messages.
Lifelines represent communication partners, while messages represent the
communication.
Interactions have no notation of their own. They are represented by the entire
diagram ( Figure 3.69 ), similar to state machines. In some cases, the diagram frame
is included in the modeling ( Figure 3.70 ).
An interaction describes a specifi c scenario. It represents the participating elements
(communication partners) and the sequence showing who sends whom
FIGURE 3-69
A sequence diagram, ???cooling soft drink.???
sd Cooling soft drink
opt
:TemperatureSensor :RefrigeratingSystem
Temperature(16)
Cooling(on)
checkTemperature()
?«system?»
:Soft-drink
vending machine
[cooling required]
205
a message and when. The concrete scenario does not have to be complete. We
model only messages that are of interest in the context of the interaction.
Sequence diagrams had not been invented together with UML. They are
based on the Message Sequence Charts ( MSC ) of the SDL ( Specifi cation and
Description Language ) modeling language [36, 37].
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