UML Weekend Crash Course™ - To Parent Directory

Session 14—Modeling the Functional View: The Activity Diagram 155
Synchronization
Synchronization
Figure 14-8 Merging control using the synchronization bar
I should point out that identifying a concurrency opportunity does not necessarily dictate
a concurrency requirement. It simply models the fact that sequential processing is not
required, and if the implementation environment supports it, there may be a chance to
optimize the performance of the application by exploiting the concurrency opportunity.
REVIEW
The Activity diagram is the UML version of the classic flowchart. It may be applied to any
process, large or small. Three common applications of flowcharts are to explain workflow (a
series of Use Cases), to explain a single Use Case, and to explain a method.
The Activity diagram represents a task as an activity drawn as a rounded rectangle
containing a freeform text description of the task. The transition from one activity
to the next is shown as an arrow. The notation provides for start and end points,
using a dot and a bull’s-eye, respectively.
Model decisions with a diamond. Each transition exiting the decision must be
labeled with a guard condition and the conditions must be mutually exclusive. The
diamond may also be used to represent a merge point, joining two alternative paths
in the sequence.
Guard conditions may also be used on transitions leaving an activity, where the result
of the activity provides all the information needed to meet one of the conditions.
Concurrency allows multiple threads or processes to execute simultaneously. The
fork bar shows one transition initiating multiple transitions. The synchronization
bar shows multiple transitions coming to an end and one new transition taking over.
QUIZ YOURSELF
1. Name two situations in which the Activity diagram is typically applied. (See
“Introducing the Activity Diagram.”)
2. What notations indicate the start and end points in an Activity diagram (See
“Start and end.”)
3. What symbol is used to show the start of concurrent processes (See “Concurrency.”)
4. How do you indicate the direction to follow out of a decision point (See “Decisions.”)
5. What is a transition (See “Activities and transitions.”)