Decisions
A system where each functionality is only a linear flow of events will be a very boring system (although I’m sure you prefer to implement such as a system). Decision nodes allows your activity to flow into different directions.
A decision node is indicated by a diamond. The diamond can also be used to merge your activity’s flow.
From this decision node, your activity can be split into multiple flows. Obviously, that cannot happen for no reason. As such you need to indicate the condition for your flow to diverge to a specific side. This condition is shown as text in square brackets on the edge. This is shown below. Here you can see that the flow diverges, based on some condition and then merges again.
After a decision node, the flow will follow only one edge. This should not be used for parallel activities.
A flow does not necessarily have to merge back. A certain condition can trigger an activity to end, as shown below.
Consider this Use Case Description:
Use Case: Update Individual Marks
1. Lecturer selects student
2. System displays relevant student’s current marks
3. Lecturer changes one or more marks
4. System validates marks
5. System stores marks
Extensions
4a. Invalid mark entered
1. System notifies Lecturer of invalid mark
2. Lecturer can fix mark or cancelThis activity shows where the System will validate the marks. If the marks are invalid, it will notify the Lecturer and then allow them to fix the marks. If the Lecturer chooses to fix the entry, the flow the returns to Change marks action, otherwise it ends. Take note how the “[reenter marks]” condition enters and exists the label “a”.
