UML Activity Diagrams show the flow of activities and processes within a system. They depict sequences, parallelism, conditional flows, and other key properties of workflows and business processes. The diagrams use common elements like initial/final activities, decisions, concurrency, and control nodes. Activity diagrams are used to model system behavior at a high level, unlike sequence diagrams which show message flows for specific use cases.

1. UML Activity Diagrams

2. Activity Diagram
• Activity is a particular operation of the system.
• An Activity diagram is a dynamic diagram that shows
the activity and the event that causes the object to
be in the particular state.
• The diagrams describe the state of activities by
showing the sequence of activities performed.
• Activity diagrams can show activities that are
conditional or parallel.

3. Activity Diagram
• The purposes of Activity diagram 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.

4. Elements in Activity Diagram
Initial Activity: This shows the starting
point or first activity of the flow. Denoted
by a solid circle. This is similar to the
notation used for Initial State.
Activity: Represented by a rectangle with
rounded (almost oval) edges.
Decisions: Similar to flowcharts, a logic
where a decision is to be made is
depicted by a diamond, with the options
written on either sides of the arrows
emerging from the diamond, within box
brackets.

5. Elements in Activity Diagram
Concurrent Activities: Some
activities occur simultaneously
or in parallel. Such activities are
called concurrent activities. For
example, listening to the
lecturer and looking at the
blackboard is a parallel activity.
This is represented by a
horizontal split (thick dark line)
and the two concurrent
activities next to each other, and
the horizontal line again to show
the end of the parallel activity.

6. Elements in Activity Diagram
• Fork and Join Nodes
Forks and joins have the same notation: either a horizontal or
vertical bar (the orientation is dependent on whether the
control flow is running left to right or top to bottom). They
indicate the start and end of concurrent threads of control.
The following diagram shows an example of their use.

7. Elements in Activity Diagram
• Decision and Merge Nodes
Decision nodes and merge nodes have the same notation: a
diamond shape. They can both be named. The control flows
coming away from a decision node will have guard conditions
which will allow control to flow if the guard condition is met.
The following diagram shows use of a decision node and a
merge node.

8. Join node vs Merge node
• A join is different from a merge in that the join
synchronizes two inflows and produces a
single outflow. The outflow from a join cannot
execute until all inflows have been received. A
merge passes any control flows straight
through it.

11. • The following diagram is drawn with the four main
activities:
• Send order by the customer
• Receipt of the order
• Confirm order
• 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.

15. Activity Diagram vs. Other Diagrams
• Other 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 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 etc.

16. Sequence diagram vs. Activity Diagram
Sequence diagrams describe interactions among
objects in terms of an exchange of messages over time.
Sequence diagrams show a detailed flow for a specific
use case or even just part of a specific use case.
Activity diagrams illustrate the dynamic nature of a
system by modeling the flow of control from activity to
activity. An activity represents an operation on some
class in the system that results in a change in the state
of the system.