Activity Diagrams

📘 Activity Diagrams (OOAD – UML)

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🔹 1. Definition

An Activity Diagram is a UML behavioral diagram that shows the flow of activities or actions in a system.

👉 Simple idea: It represents step-by-step workflow of a process, like a flowchart but more powerful in OOAD.

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🔹 2. Purpose of Activity Diagrams

• Show workflow of a system
• Model business processes
• Describe step-by-step execution
• Help in understanding system behavior
• Useful for analysis and design

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🔹 3. Key Idea ⭐

• Focuses on activities (actions/tasks)
• Shows control flow and decision making
• Can represent both simple and complex processes

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🔹 4. Basic Notation

Symbol	Meaning
●	Initial state (Start)
◎	Final state (End)
▭	Activity (Action)
→	Flow (Transition)
◇	Decision (if/else)
			Fork/Join (parallel processing)

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🔹 5. Components of Activity Diagram

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🔸 5.1 Activity

• Represents a task or action Example: Login, Process Payment

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🔸 5.2 Transition (Flow)

• Shows movement from one activity to another

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🔸 5.3 Decision Node

• Represents if-else condition

Example:

Login successful? → Yes / No

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🔸 5.4 Initial Node

• Starting point (●)

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🔸 5.5 Final Node

• Ending point (◎)

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🔸 5.6 Fork and Join

• Used for parallel activities

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🔹 6. Example (ATM System) ⭐

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🔹 Steps:

1. Insert Card
2. Enter PIN
3. Verify PIN
4. Choose Transaction
5. Withdraw / Check Balance
6. End Transaction

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🔹 Activity Flow:

● → Insert Card → Enter PIN → Verify PIN
          ↓
     [Decision]
   Yes        No
   ↓           ↓
Transaction   Exit
   ↓
◎

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🔹 7. Example (Online Shopping)

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🔹 Flow:

1. Login
2. Search Product
3. Add to Cart
4. Checkout
5. Payment
6. Order Confirmed

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🔹 8. Types of Activity Nodes

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🔸 8.1 Simple Activity

• Single step action

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🔸 8.2 Composite Activity

• Group of activities

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🔸 8.3 Concurrent Activity

• Multiple tasks happen simultaneously

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🔹 9. Activity Diagram vs Flowchart

Feature	Activity Diagram	Flowchart
Standard	UML standard	General tool
Focus	Object-oriented system	Simple process
Parallelism	Supported	Limited
Usage	Software design	General logic

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🔹 10. Advantages of Activity Diagrams

• Easy to understand workflows
• Models complex processes clearly
• Supports parallel processing
• Helps in system analysis
• Useful for business modeling

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🔹 11. Important Rules / Guidelines

• Start with initial node (●)
• End with final node (◎)
• Use clear and simple activities
• Avoid too many complex branches
• Ensure logical flow

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🔹 12. Where Activity Diagrams are Used

• ATM systems
• Online shopping
• Banking systems
• Login processes
• Order processing systems

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🔹 13. Likely Exam Questions

1. Define activity diagram.
2. Explain components of activity diagram.
3. Draw activity diagram of ATM system.
4. Difference between activity diagram and flowchart.
5. What is a decision node?
6. Explain fork and join.
7. Advantages of activity diagrams.
8. Explain login process using activity diagram.
9. What are initial and final nodes?
10. Role of activity diagrams in OOAD.

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🔹 14. Quick Revision Summary 🧠

• Activity Diagram = Workflow of system

• Shows:

  • Activities
  • Decisions
  • Flow of control
  • Parallel actions

👉 Trick to Remember: "ADF" → Activity, Decision, Flow

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