Relationships (association, aggregation, composition) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the type of relationship in a library system

In a library system, a Book can be borrowed by many Members, and a Member can borrow many Books. What type of relationship is this?

A Association

B Aggregation

C Inheritance

D Composition

💡 Hint

Think about whether the objects can exist independently.

This is an association because both Book and Member can exist independently and are linked by borrowing.

❓ Architecture

intermediate

Choose the correct relationship for a car and its engine

A Car has an Engine. The engine can exist independently and can be replaced. What is the correct relationship between Car and Engine?

A Dependency

B Composition

C Association

D Aggregation

💡 Hint

Consider if the engine can exist without the car.

Aggregation is correct because the engine can exist independently and is part of the car but not owned exclusively.

❓ scaling

advanced

Impact of composition on object lifecycle in a social media app

In a social media app, a UserProfile contains ProfilePicture as a part of it. If the UserProfile is deleted, the ProfilePicture is also deleted. What is the impact of this composition relationship on system design when scaling?

A It allows independent scaling of ProfilePicture storage.

B It simplifies cleanup but requires careful cascading deletes in the database.

C It requires ProfilePicture to be cached separately for performance.

D It means ProfilePicture can be shared among multiple UserProfiles.

💡 Hint

Think about ownership and lifecycle dependency.

Composition means the ProfilePicture lifecycle depends on UserProfile, so deleting UserProfile must also delete ProfilePicture, requiring cascading deletes.

❓ tradeoff

advanced

Choosing between aggregation and composition for a shopping cart system

In a shopping cart system, a ShoppingCart contains multiple Items. Items can exist without the cart and can be added to multiple carts. Which relationship is best and why?

A Aggregation, because items can exist independently and be shared.

B Composition, because items belong exclusively to one cart.

C Association, because items and carts have no ownership.

D Inheritance, because items are a type of cart element.

💡 Hint

Consider if items can be shared or must be owned exclusively.

Aggregation fits because items exist independently and can be shared among carts, unlike composition which implies exclusive ownership.

❓ component

expert

Designing a document editor with embedded images: relationship choice

You are designing a document editor where a Document contains multiple EmbeddedImages. EmbeddedImages cannot exist outside the document and are deleted when the document is deleted. However, images can be large and stored separately for performance. Which relationship best models this scenario and why?

A Dependency, because images are only used temporarily during editing.

B Aggregation, because images are stored separately and can exist independently.

C Composition, because EmbeddedImages lifecycle depends on Document.

D Association, because images and documents are loosely connected.

💡 Hint

Think about ownership and lifecycle dependency despite storage separation.

Composition is correct because EmbeddedImages cannot exist without the Document, even if stored separately, their lifecycle is tied to the Document.