Interactions between objects are represented by interaction diagrams — both sequence and collaboration diagrams. An example of a collaboration diagram is shown here: Objects are drawn as rectangles and the lines between them indicate links — a link is an instance of an association. The number at the head of the message indicates the order of the messages along the links between the objects.
Sequence diagrams show essentially the same information, but concentrate on the time-ordered communication between objects, rather than their relationships. An example of a sequence diagram is shown here:
The dashed vertical lines represent the lifeline of the object (starting at the top).
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