Activity Diagram

Activity Diagram

• An Activity diagram is designed to be a simplified look at what happens during an operation or a process.
• An Activity diagram highlights the activities/operation.
• It describes the sequencing of activities, with support for both conditional and parallel behavior.
• They are used to explore the logic of :
•  A complex operation
•  A complex business rule
•  A single use case
•  Several use cases
•  A Business process 
• Used in Analysis and Design phase to depict a business workflow.

Should be used for :

• Analyzing a use case
  At this stage, one is not interested in allocating actions to objects instead, we need to understand what actions need to take place –

• Understanding Workflow
  Activity diagrams are very useful for understanding the business process.

• Describing a complicated sequential algorithm
  In this case, an activity diagram is really nothing more than a UML-compliant flowchart.

Should not be used for :

• Trying to see how objects collaborate.
• Trying to see how an object behaves over its lifetime.

Parts of an activity diagram

• Decision-Making Activities
• Concurrent Paths / Parallel Activities
• Dynamic Concurrency
• Swim lanes

Decision-Making Activities

• Also called branch
• Two or more mutually exclusive transitions, each having a guard expression
• Every branch has its subsequent merge, where the exclusive transitions combine
• Appear in the diagram as hollow diamonds

Concurrent Paths / Parallel Activities

• FORK: One transition entering and two or more transitions leaving it
• JOIN: Two or more transitions entering it and Only one leaving it
• In general, for every Fork, there is a Join
• Forks have only One Entry Transition
• Joins have One Exit Transition

Dynamic Concurrency

Shows iterations without having to construct a loop

Swim lanes

• Arranges activity diagrams into vertical zones separated by lines
• Each zone represents the responsibilities of a particular class or department
• Tells about which object is responsible for which activity

Example

Exercise

• Customer call to Request Service
• Upon completion of this operation, the customer pays, and the sales and stockroom staff take and fill the customer's order simultaneously.
• Parallel processes to indicate that when the customer has paid and the order has been filled, then the order is ready for delivery.
• After the delivery of the order, the customer can collect the order, and the process is complete.