Actions are
denoted with a fork symbol in the lower right-hand corner. If this call is synchronous,
then this means for the execution that the called activity is terminated as
soon as the call terminates. This corresponds to the semantics of a composition
between classes.
You can represent object nodes in an activity as well. This is an association,
rather than a composition, from the activity to the element that describes the type
of object node (e.g., a block) such as customer in Figure 4.48 .
You should select a diagram layout that matches a tree structure. The action
that invokes the activity is the role name at the composition end in this representation.
In practice, activity names and action names are normally identical. In this
case you can omit the role name.
Note, however, that this works only with activities. An action is formally not
related to the class, so that it cannot become a node or leaf in the function tree.
This means, for example, that confi rm usage start in Figure 4.48 would actually
be illegal. We can solve this problem with a modeling trick: We introduce an activity
that includes only one single action ( Figure 4.
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