UML Activity Diagram
1. Overview:
Activity
diagram is another important diagram in UML to describe dynamic aspects of the
system.
Activity
diagram is basically a flow chart to represent the flow form one activity to
another activity. The activity can be described as an operation of the system.
So
the control flow is drawn from one operation to another. This flow can be
sequential, branched or concurrent. Activity diagrams deals with all type of
flow control by using different elements like fork, join etc.
2. Purpose:
The
basic purposes of activity diagrams are similar to other four diagrams. It
captures the dynamic behaviour of the system. Other four diagrams are used to
show the message flow from one object to another but activity diagram is used
to show message flow from one activity to another
Activity
is a particular operation of the system. Activity diagrams are not only used for
visualizing dynamic nature of a system but they are also used to construct the
executable system by using forward and reverse engineering techniques. The only
missing thing in activity diagram is the message part.
It
does not show any message flow from one activity to another. Activity diagram
is some time considered as the flow chart. Although the diagrams looks like a
flow chart but it is not. It shows different flow like parallel, branched,
concurrent and single.
So
the purposes can be described as:
Draw
the activity flow of a system.
Describe
the sequence from one activity to another.
Describe
the parallel, branched and concurrent flow of the system.
How
to draw Component Diagram?
Activity
diagrams are mainly used as a flow chart consists of activities performed by
the system. But activity diagram are not exactly a flow chart as they have some
additional capabilities. These additional capabilities include branching,
parallel flow, swimlane etc.
Before
drawing an activity diagram we must have a clear understanding about the
elements used in activity diagram. The main element of an activity diagram is
the activity itself. An activity is a function performed by the system. After
identifying the activities we need to understand how they are associated with
constraints and conditions.
So
before drawing an activity diagram we should identify the following elements:
1. Activities
2. Association
3. Conditions
4. Constraints
Once
the above mentioned parameters are identified we need to make a mental layout
of the entire flow. This mental layout is then transformed into an activity
diagram.
The
following is an example of an activity diagram for order management system. In
the diagram four activities are identified which are associated with
conditions. One important point should be clearly understood that an activity
diagram cannot be exactly matched with the code. The activity diagram is made
to understand the flow of activities and mainly used by the business users
The
following diagram is drawn with the four main activities:
1. Send
order by the customer
2. Receipt
of the order
3. Confirm
order
4. Dispatch
order
After
receiving the order request condition checks are performed to check if it is
normal or special order. After the type of order is identified dispatch
activity is performed and that is marked as the termination of the process.
Where
to use Interaction Diagrams?
The
basic usage of activity diagram is similar to other four UML diagrams. The
specific usage is to model the control flow from one activity to another. This
control flow does not include messages.
The
activity diagram is suitable for modeling the activity flow of the system. An
application can have multiple systems. Activity diagram also captures these
systems and describes flow from one system to another. This specific usage is
not available in other diagrams. These systems can be database, external queues
or any other system.
Now
we will look into the practical applications of the activity diagram. From the
above discussion it is clear that an activity diagram is drawn from a very high
level. So it gives high level view of a system. This high level view is mainly
for business users or any other person who is not a technical person.
This
diagram is used to model the activities which are nothing but business
requirements. So the diagram has more impact on business understanding rather
implementation details.
Following
are the main usages of activity diagram:
1. Modeling
work flow by using activities.
2. Modeling
business requirements.
3. High
level understanding of the system's functionalities.
4. Investigate
business requirements at a later stage
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