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There is exactly one incoming edge and an arbitrary number
of outgoing edges, which each have a condition.
A merge node is a node in an activity at which several fl ows are merged into
one single fl ow. There is an arbitrary number of incoming edges and exactly
one outgoing edge.
A flow within an activity is generally controlled by conditions. If XY is true, then
do A , otherwise do B . What we need for this is a decision node. The notation is a
186 CHAPTER 3 UML??”Unifi ed Modeling Language
rhombus with one incoming edge and an arbitrary number of outgoing edges, at
which there is a condition each within brackets ( Figure 3.49 ).
A condition is a Boolean expression in any language. 13 Never more than one
condition may be true. Also, exactly one condition must always be met. We can
use the [else] condition to ensure this. This way is always chosen when all other
conditions are false ( Figure 3.49 ).
The notation for merge nodes is the same as that for decision nodes. A merge
node is the counterpart that merges several optional fl ows into one single fl ow.


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