Identifying classes from requirements in LLD - System Design Exercise

Design: Class Identification from Requirements

Focus on identifying classes, their attributes, methods, and relationships from textual requirements. Out of scope: detailed implementation or database design.

Functional Requirements

FR1: Analyze given software requirements to find key entities.

FR2: Determine attributes and behaviors for each entity.

FR3: Establish relationships between entities.

FR4: Create a clear class diagram representing the system structure.

Non-Functional Requirements

NFR1: Classes must represent real-world concepts or system components.

NFR2: Relationships must be accurate (inheritance, association, aggregation, composition).

NFR3: Design should be simple and understandable for beginners.

NFR4: Support scalability for future system expansion.

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

Entities as classes

Attributes as class properties

Methods as class behaviors

Relationships like inheritance and associations

Design Patterns

Single Responsibility Principle

Encapsulation

Inheritance and Polymorphism

Association, Aggregation, Composition

Reference Architecture

Requirements Text
      |
      v
  Identify Nouns (Entities) ---> Define Classes
      |                             |
      v                             v
  Identify Verbs (Behaviors)    Define Attributes
      |                             |
      v                             v
  Establish Relationships <-------
      |
      v
  Draw Class Diagram

Components

Class

UML/OO Design

Represents an entity with attributes and behaviors.

Attribute

UML/OO Design

Describes properties or data held by a class.

Method

UML/OO Design

Defines actions or behaviors of a class.

Relationship

UML/OO Design

Shows how classes connect (inheritance, association, etc.).

Request Flow

1. Read the software requirements text.

2. Extract nouns to identify potential classes.

3. Extract verbs to identify methods or behaviors.

4. Determine attributes from descriptive phrases.

5. Analyze relationships between classes (e.g., 'is a', 'has a').

6. Create a class diagram showing classes, attributes, methods, and relationships.

Database Schema

Not applicable; focus is on class identification and relationships, not database design.

Scaling Discussion

Bottlenecks

Complex requirements with many entities can cause confusion.

Ambiguous or incomplete requirements lead to incorrect class identification.

Overlapping responsibilities among classes reduce clarity.

Ignoring relationships can cause poor system structure.

Solutions

Break down requirements into smaller parts and analyze separately.

Clarify ambiguous requirements with stakeholders.

Apply design principles like Single Responsibility Principle.

Use iterative refinement and peer reviews of class diagrams.

Interview Tips

Time: Spend 10 minutes understanding requirements and identifying nouns and verbs, 15 minutes defining classes and relationships, and 5 minutes reviewing and explaining the class diagram.

Explain how you identify classes from nouns in requirements.

Describe how verbs help define class behaviors (methods).

Discuss how you determine relationships between classes.

Mention design principles used to keep classes focused and maintainable.

Highlight importance of iterative refinement and communication.