In contrast to other UML behavior elements, however, an activity has its own
notation: a rectangle with rounded corners. Its name is in the upper left corner, and
the upper right corner can be used to optionally write preconditions or postconditions.
The remaining area is used to describe the flow, including nodes and edges. The
activity rectangle is omitted in combination with the diagram frame ( Figure 3.35 ).
A precondition begins with the keyword ?«precondition?» and is written in
the upper right corner of the activity ( Figure 3.35 ). The condition itself can be an
arbitrary Boolean expression (e.g., in OCL 11 ) in a programming language, or in a
natural language. The activity starts only provided that the precondition is met.
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A postcondition is preceded with the keyword ?«postcondition?» ( Figure 3.35 ).
It is always deemed to have been met upon termination of the activity.
Input parameters are used so that the caller of the activity can initially transmit
data. Output parameters are used so that the activity can return data outwards to
the caller upon termination.
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