BABOK_Guide_v3_member_copy

Sequence Diagrams
Techniques
10.42.3 Elements
the next are represented as horizontal arrows. The order of the messages is
represented in a top-down and left-to-right sequence beginning with the first
message at the top left of the page and subsequent messages occurring to the
right and below. Sequence diagrams are sometimes called event diagrams.
The standard notation for sequence diagrams is defined as part of the Unified
Modelling Language (UML ® ) specification.
.1 Lifeline
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A lifeline represents the lifespan of an object during the scenario being modelled
in a sequence diagram. The example below shows the object order. A lifeline is
drawn as a dashed line that vertically descends from each object box to the
bottom of the page.
Figure 10.42.1: Lifeline
.2 Activation Box
An activation box represents the period during which an operation is executed. A
call to activate is represented by an arrow with a solid arrowhead leading to the
activation object. The lifeline can be terminated with an X.
Figure 10.42.2: Activation Box
.3 Message
A message is an interaction between two objects. A message is shown as an
arrow coming from the activation box of the object that sends the message to the
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