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Activity Diagram

Activity Diagram

What is an Activity Diagram?

  • Activity Diagram is on of the UML diagrams for modeling the dynamic aspects of the system.
  • Activity diagram is drawn only from the system perspective.
  • It is type of flow chat where the flow of control is from one activity to the other.
  • An Activity is the function performed by the system.
  • Activity diagram is not only important for modeling the dynamic aspect of a system but also for constructing executable systems.

Steps to draw an activity diagram

Step 1: Identify the base activity.

Step 2: Identify the actives before the base activity.

Step 3:identify the actives after the base activity.

Step 4:Identify conditions.

Step 5: identify Events(Time schedule)

Activity Diagram will have the following elements:


  • Start Node:

Represent the initiation of a process, that is where the workflow begins


  • Final Node:

Represents the completion of a process.


  • Activity:

Represent the activity.


  • Control Flow:

Represent the direction flow of the process.


  • Fork & Join:

This is used for parallel activities. A fork indicated the point after which a number of actives may begging in any order. A join indicated that the workflow may commence only once the parallel actives that flow into it have all been completed.

  • Guard Condition:

It is a condition attached to the control flow, when the guard condition is true workflow may flow along the control flow. It is show within square brackets.


  • Decision:

It has at least 2 paths coming out of the decision node which tells you which direction to move forward based on the guard condition.


  • Branch & Merge:
    Branching :Opted when you want one sequence to be divided into several alternatives. For example Mode of payment while placing an order in an E-commerce website: Debit Card, Internet Banking, Wallet.
    Merging: Opted when several flows lead to the same activity. For example After the payment is done among one of the mode of payment, all leads to the successful completion of a payment and proceeds with placement of an order in an E-commerce application.


  • Event:

A trigger attached to a control flow An event must occur for the flow to move along the  control flow.


Thing to remember while drawing an activity diagram


  • All the activities should be from system perspective.
  • Actives are time bounded.
  • Number of flows that enter during fork should be equal to the number of flows leaving at the time of join.
  • All the possible conditions must be included without fail.


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