Room type hierarchy in LLD - Architecture Diagram

System Overview - Room type hierarchy

This system models a hierarchy of room types for a building or hotel management application. It organizes rooms into categories and subcategories to allow easy classification and retrieval based on features or usage.

Key requirements include supporting inheritance of properties from parent room types and enabling efficient queries for room details.

Architecture Diagram

User
  |
  v
Room Type Service
  |
  v
Room Type Hierarchy Store
  |
  +--> Cache
  |
  +--> Database

Components

User

user

Initiates requests to query or manage room types

Room Type Service

service

Handles business logic for room type hierarchy management and queries

Room Type Hierarchy Store

logical_store

Abstracts storage of room type data with hierarchy relationships

Cache

cache

Stores frequently accessed room type data for fast retrieval

Database

database

Persistent storage of room type hierarchy and details

Request Flow - 7 Hops

User → Room Type Service

Room Type Service → Cache

Cache → Room Type Service

Room Type Service → Database

Database → Room Type Service

Room Type Service → Cache

Room Type Service → User

Failure Scenario

Component Fails:Cache

Impact:Cache misses increase, causing more database queries and higher latency

Mitigation:System continues to function by querying database directly; cache rebuilds on requests

Architecture Quiz - 3 Questions

Which component is responsible for storing the persistent room type hierarchy?

A Cache

B Database

C Room Type Service

D User

Design Principle

This design uses a cache to speed up frequent room type queries, reducing load on the database and improving response times. The hierarchy is stored persistently in the database, while the service layer manages business logic and data retrieval.

Practice

1. What is the main purpose of using a Room type hierarchy in system design?

easy

A. To randomly assign room types without any structure

B. To organize rooms by shared and unique features for easier maintenance

C. To store all room data in a single flat list without categories

D. To duplicate room properties in every class separately

Solution

1. Step 1: Understand the concept of hierarchy

   A hierarchy groups items by common traits, making management simpler.

2. Step 2: Apply to room types

   Using a base class for shared features and subclasses for specifics avoids duplication and eases updates.

3. Final Answer:

   To organize rooms by shared and unique features for easier maintenance -> Option B

4. Quick Check:

   Hierarchy = Organize by features [OK]

Hint: Think: shared features go in base, unique in subclasses [OK]

Common Mistakes:

• Confusing hierarchy with flat lists
• Duplicating properties in every room class
• Ignoring shared features in base class

2. Which of the following is the correct way to define a base class Room with a subclass ConferenceRoom in a typical object-oriented design?

easy

A. class Room {}; class ConferenceRoom extends Room {}

B. class Room; class ConferenceRoom inherits Room

C. class Room() {}; class ConferenceRoom() inherits Room()

D. class Room {}; class ConferenceRoom inherits Room {}

Solution

1. Step 1: Identify correct syntax for inheritance

   In many modern languages, extends is used to inherit from a base class.

2. Step 2: Check each option

   class Room {}; class ConferenceRoom extends Room {} uses correct syntax: class ConferenceRoom extends Room {}. Others use incorrect or incomplete syntax.

3. Final Answer:

   class Room {}; class ConferenceRoom extends Room {} -> Option A

4. Quick Check:

   Inheritance syntax = extends [OK]

Hint: Remember: subclass extends base class in OOP [OK]

Common Mistakes:

• Using 'inherits' instead of 'extends'
• Missing curly braces for class body
• Incorrect parentheses in class declaration

3. Given this Python-like pseudocode for room types:

class Room:
    def __init__(self, name):
        self.name = name

class Bedroom(Room):
    def __init__(self, name, bed_size):
        super().__init__(name)
        self.bed_size = bed_size

room = Bedroom('Master', 'King')
print(room.name, room.bed_size)

What will be the output?

medium

A. Error: missing argument

B. Bedroom King

C. Master None

D. Master King

Solution

1. Step 1: Trace object creation

   Creating Bedroom('Master', 'King') calls Bedroom's constructor, which calls Room's constructor with 'Master'.

2. Step 2: Check printed attributes

   room.name is 'Master' from Room; room.bed_size is 'King' from Bedroom.

3. Final Answer:

   Master King -> Option D

4. Quick Check:

   Subclass calls base, attributes set correctly [OK]

Hint: Remember: super() sets base class attributes [OK]

Common Mistakes:

• Assuming subclass overwrites base attributes
• Forgetting to call super().__init__
• Confusing attribute names

4. Consider this code snippet for a room hierarchy:

class Room:
    def __init__(self, name):
        self.name = name

class MeetingRoom(Room):
    def __init__(self, name, capacity):
        self.capacity = capacity

room = MeetingRoom('Boardroom', 20)
print(room.name, room.capacity)

What is the issue here?

medium

A. capacity attribute is not set correctly

B. Syntax error in class definition

C. Missing call to base class constructor causes room.name to be undefined

D. No issue; code runs fine

Solution

1. Step 1: Check constructor chaining

   MeetingRoom's constructor sets capacity but does not call super().__init__(name), so name is not set.

2. Step 2: Understand effect on attributes

   Without base constructor call, room.name is missing, causing error or undefined behavior.

3. Final Answer:

   Missing call to base class constructor causes room.name to be undefined -> Option C

4. Quick Check:

   Always call base __init__ in subclass [OK]

Hint: Call super().__init__ to set base attributes [OK]

Common Mistakes:

• Assuming base constructor runs automatically
• Ignoring missing attributes in subclass
• Confusing syntax errors with logic errors

5. You need to design a room type hierarchy for a hotel system that includes Room, Bedroom, ConferenceRoom, and Suite. Suites can have multiple bedrooms and a living area. Which design approach best models this?

hard

A. Make Suite inherit from Room and include a list of Bedroom objects plus living area

B. Make Suite inherit from Bedroom and add living area attributes

C. Make Suite a separate class unrelated to Room hierarchy

D. Make Bedroom inherit from Suite to reuse features

Solution

1. Step 1: Analyze relationships

   Suite is a special Room that contains multiple Bedrooms and a living area, so it should inherit from Room.

2. Step 2: Model composition

   Suite should have a list of Bedroom objects (composition) to represent multiple bedrooms, plus its own living area attributes.

3. Final Answer:

   Make Suite inherit from Room and include a list of Bedroom objects plus living area -> Option A

4. Quick Check:

   Use inheritance + composition for complex types [OK]

Hint: Use composition for multiple rooms inside Suite [OK]

Common Mistakes:

• Using inheritance to model 'has-many' relationships
• Ignoring composition for complex room types
• Making unrelated classes inherit incorrectly