Inheritance and interface notation in LLD - System Design Exercise

Design: Inheritance and Interface Notation System

Focus on notation and diagram representation of inheritance and interfaces. Implementation details of classes or methods are out of scope.

Functional Requirements

FR1: Represent class inheritance relationships clearly

FR2: Represent interface implementation relationships

FR3: Support multiple inheritance where allowed

FR4: Show abstract classes and interfaces distinctly

FR5: Allow notation for method overriding and interface methods

FR6: Be understandable by developers with basic OOP knowledge

Non-Functional Requirements

NFR1: Notation must be simple and unambiguous

NFR2: Must scale to diagrams with up to 50 classes/interfaces

NFR3: Should be usable in low-fidelity design tools (e.g., whiteboard, paper)

NFR4: Latency and availability not applicable

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

Class boxes with name and stereotype

Arrows for inheritance (solid line with closed arrowhead)

Dashed arrows for interface implementation

Labels or stereotypes for abstract classes and interfaces

Method lists inside class/interface boxes

Design Patterns

UML class diagram notation

Use of stereotypes like <<interface>>, <<abstract>>

Arrow styles for inheritance vs implementation

Notation for method overriding

Separation of interface and implementation

Reference Architecture

  +----------------+          +----------------+
  | <<abstract>>   |          | <<interface>>  |
  |   Animal       |          |   Movable      |
  |----------------|          |----------------|
  | +eat()         |          | +move()        |
  +-------^--------+          +-------^--------+
          |                           |
          | inherits                  | implements
  +-------+--------+          +-------+--------+
  |   Dog          |          |   Car          |
  |----------------|          |----------------|
  | +bark()        |          | +drive()       |
  +----------------+          +----------------+

Components

Class Box

Diagram element

Represents a class or interface with name and methods

Inheritance Arrow

Solid line with closed arrowhead

Shows class inheritance relationship

Interface Implementation Arrow

Dashed line with closed arrowhead

Shows a class implements an interface

Stereotypes

Text labels like <<interface>>, <<abstract>>

Distinguish interfaces and abstract classes

Request Flow

1. 1. Identify all classes and interfaces to represent.

2. 2. Draw boxes for each class/interface with name and methods.

3. 3. Add stereotype labels to indicate abstract or interface.

4. 4. Connect classes with solid arrows to show inheritance.

5. 5. Connect classes to interfaces with dashed arrows for implementation.

6. 6. Use method lists to show overridden or interface methods.

Database Schema

Not applicable for notation system; focus is on diagram elements and relationships.

Scaling Discussion

Bottlenecks

Diagram clutter with many classes and interfaces

Difficulty distinguishing multiple inheritance arrows

Confusion between inheritance and implementation arrows

Limited space for method details in boxes

Solutions

Group related classes into packages or modules

Use color coding or different arrow thickness for clarity

Provide legend explaining arrow styles and stereotypes

Use expandable/collapsible sections for method lists

Interview Tips

Time: Spend 10 minutes clarifying requirements and constraints, 20 minutes drawing and explaining notation, 15 minutes discussing scaling and alternatives.

Explain difference between inheritance and interface implementation

Show how notation distinguishes abstract classes and interfaces

Discuss arrow styles and stereotypes for clarity

Mention how to handle complexity in large diagrams

Relate notation to common UML standards for familiarity