[Solved] Which design approach best models the relationship between Books, Copies, and Loans in a Library Management System to handle multiple copies of the same book being loaned independently? | OOP & Design Patterns

OOP & Design Patterns - Design a Library Management System - LLD with Relationships & Edge Cases

Which design approach best models the relationship between Books, Copies, and Loans in a Library Management System to handle multiple copies of the same book being loaned independently?

AUse inheritance where Copy inherits from Book and Loan inherits from Copy

BUse composition where Book contains multiple Copy objects, and each Copy can have zero or one Loan

CUse aggregation where Loan aggregates Book and Copy directly without intermediate objects

DUse a flat structure where Book, Copy, and Loan are unrelated classes with independent lifecycles

Step-by-Step Solution

Solution:

Step 1: Understand the domain relationships between Book, Copy, and Loan
A Book can have multiple physical Copies; each Copy can be loaned independently.
Step 2: Evaluate inheritance versus composition for modeling relationships
Inheritance is inappropriate because a Copy is not a specialized Book but a part of it; composition models "has-a" relationships correctly.
Step 3: Analyze aggregation and flat structure drawbacks
Aggregation without Copy as an intermediate loses clarity; flat structure ignores relationships and lifecycle dependencies.
Final Answer:
Option B -> Option B
Quick Check:
Composition models multiple copies and loans accurately [OK]

Quick Trick: Copies are parts of Books -> composition fits best [OK]

Common Mistakes:

MISTAKES

Using inheritance for Copy from Book
Ignoring Copy as a separate entity
Flattening relationships losing lifecycle control

Trap Explanation:

PITFALL

Candidates often misuse inheritance for 'part-of' relationships, leading to poor design and confusion.

Interviewer Note:

CONTEXT

Reveals understanding of class relationships and composition vs inheritance.

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More OOP & Design Patterns Quizzes

Which design approach best models the relationship between Books, Copies, and Loans in a Library Management System to handle multiple copies of the same book being loaned independently?

Step 1: Understand the domain relationships between Book, Copy, and Loan

Step 2: Evaluate inheritance versus composition for modeling relationships

Step 3: Analyze aggregation and flat structure drawbacks

Final Answer:

Quick Check:

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