📘 Requirements Engineering: Use Cases & Prototyping (OOAD)

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🔹 1. Definition of Requirements Engineering

Requirements Engineering (RE) is the process of collecting, analyzing, documenting, and validating what a software system should do.

👉 Simple idea: It answers: “What does the user want?”

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🔹 2. Key Activities in Requirements Engineering

1. Elicitation → Gathering requirements
2. Analysis → Understanding and refining
3. Specification → Documenting clearly
4. Validation → Checking correctness

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⭐ PART A: USE CASES

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🔹 3. What is a Use Case?

A Use Case describes how a user (actor) interacts with a system to achieve a specific goal.

👉 It shows functional requirements in a simple way.

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🔹 4. Components of a Use Case

Component	Description
Actor	User or external system
Use Case	Function (e.g., Login, Withdraw Cash)
System	The software being developed
Scenario	Step-by-step interaction

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🔹 5. Use Case Diagram (UML)

Definition: A graphical representation of actors and their interactions with the system.

Diagram Description:

• Stick figures → Actors
• Ovals → Use cases
• Lines → Interaction

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🔹 6. Types of Actors

• Primary Actor: Initiates interaction
• Secondary Actor: Supports the system

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🔹 7. Relationships in Use Cases

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🔸 7.1 Include Relationship

• One use case always includes another

Example:

Withdraw Money → includes → Authenticate User

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🔸 7.2 Extend Relationship

• Optional behavior

Example:

Login → extends → Two-Factor Authentication

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🔸 7.3 Generalization

• Inheritance among actors/use cases

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🔹 8. Use Case Scenario (Step-by-Step)

👉 Example: ATM Withdraw Money

1. User inserts card
2. System asks for PIN
3. User enters PIN
4. System verifies
5. User selects withdraw
6. Cash is dispensed

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🔹 9. Advantages of Use Cases

• Easy to understand
• Focus on user perspective
• Helps in communication
• Identifies system functionality

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⭐ PART B: PROTOTYPING

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🔹 10. What is Prototyping?

Prototyping is the process of creating a working model (sample system) to understand and refine requirements.

👉 Simple idea: Build a small version first, improve later.

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🔹 11. Types of Prototypes

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🔸 11.1 Throwaway (Rapid) Prototype

• Built quickly and discarded
• Used to understand requirements

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🔸 11.2 Evolutionary Prototype

• Continuously refined into final system

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🔸 11.3 Incremental Prototype

• Built in parts/modules

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🔹 12. Prototyping Process

Identify Requirements → Build Prototype → User Evaluation → Refine → Final System

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🔹 13. Advantages of Prototyping

• Early user feedback
• Reduces misunderstanding
• Improves system usability
• Detects errors early

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🔹 14. Disadvantages of Prototyping

• Can increase cost/time if misused
• Users may expect final system too early
• Poor design if rushed

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🔹 15. Use Cases vs Prototyping

Feature	Use Cases	Prototyping
Focus	Functional behavior	System appearance & interaction
Form	Text/Diagram	Working model
Purpose	Understanding requirements	Validating requirements

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🔹 16. Example (Library System)

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🔹 Use Case:

• Actor: Member
• Use Case: Borrow Book

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🔹 Prototype:

• Simple UI showing:

  • Book search
  • Borrow button

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🔹 17. Important Rules / Tips

• Use cases should be clear and simple
• Focus on user goals
• Prototype should be quick and flexible
• Always get user feedback

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🔹 18. Likely Exam Questions

1. Define Requirements Engineering.
2. What is a Use Case? Explain with example.
3. Draw and explain a Use Case Diagram.
4. Explain include and extend relationships.
5. What is prototyping?
6. Types of prototypes in software development.
7. Advantages and disadvantages of prototyping.
8. Difference between use cases and prototyping.
9. Explain ATM use case scenario.
10. Describe the prototyping process.

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🔹 19. Quick Revision Summary 🧠

• Requirements Engineering = Understanding user needs

Use Cases:

• Actor + Interaction
• Show system functionality
• Include, Extend relationships

Prototyping:

• Early working model

• Types:

  • Throwaway
  • Evolutionary
  • Incremental

👉 Trick to Remember: "UP" → Use Cases + Prototyping

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