Class design (Book, Member, Librarian, Loan) in LLD - Architecture Diagram

System Overview - Class design (Book, Member, Librarian, Loan)

This system models a library management scenario. It manages books, members who borrow books, librarians who manage the library, and loans that track book borrowing. The key requirements are to track book availability, member borrowing history, and librarian actions.

Architecture Diagram

  +---------+       +-----------+       +----------+       +----------+
  |  Member |<----->|   Loan    |<----->|   Book   |       | Librarian|
  +---------+       +-----------+       +----------+       +----------+
       ^                 ^                  ^                 ^
       |                 |                  |                 |
       +-----------------+------------------+-----------------+

Components

Book

class

Represents a book with details like title, author, and availability.

Member

class

Represents a library member who can borrow books.

Librarian

class

Represents a librarian who manages books and loans.

Loan

class

Tracks the borrowing of a book by a member including loan dates.

Request Flow - 5 Hops

Member → Loan

Loan → Book

Book → Loan

Loan → Member

Librarian → Book

Failure Scenario

Component Fails:Loan

Impact:New borrow requests cannot be processed, loan records cannot be created or updated.

Mitigation:System queues borrow requests and alerts librarian to fix loan system; members can still view book and member info.

Architecture Quiz - 3 Questions

Which class is responsible for tracking when a book is borrowed?

A Loan

B Book

C Member

D Librarian

Design Principle

This design separates concerns by using distinct classes for books, members, librarians, and loans. It models real-world roles and actions clearly, enabling easy tracking of book borrowing and management.

Practice

1. Which class should be responsible for storing information about a book's title, author, and ISBN in a library system?

easy

A. Member

B. Book

C. Librarian

D. Loan

Solution

1. Step 1: Identify the class representing a book

   The class named Book logically holds details about books such as title, author, and ISBN.

2. Step 2: Confirm other classes' roles

   Member is for library users, Librarian manages operations, and Loan tracks borrowing, so they don't store book details.

3. Final Answer:

   Book -> Option B

4. Quick Check:

   Book class stores book info [OK]

Hint: Book class holds book details like title and author [OK]

Common Mistakes:

• Confusing Member with Book class
• Assigning book details to Loan class
• Thinking Librarian stores book info

2. Which of the following is the correct way to define a method named borrowBook inside the Member class in Python?

easy

A. def borrowBook():

B. def borrowBook(book):

C. def borrowBook(self):

D. def borrowBook(self, book):

Solution

1. Step 1: Understand method definition in Python classes

   Instance methods must have self as the first parameter to access object data.

2. Step 2: Check method parameters for borrowing a book

   The method needs the book to borrow, so it should accept a book parameter after self.

3. Final Answer:

   def borrowBook(self, book): -> Option D

4. Quick Check:

   Instance method with self and book param [OK]

Hint: Instance methods always start with self parameter [OK]

Common Mistakes:

• Omitting self parameter
• Not passing book argument
• Defining method without parameters

3. Given the following Python code snippet, what will be the output?

class Loan:
    def __init__(self, book, member):
        self.book = book
        self.member = member

loan = Loan('1984', 'Alice')
print(loan.book, loan.member)

medium

A. 1984 Alice

B. book member

C. Loan object memory address

D. Error: missing parameters

Solution

1. Step 1: Analyze the Loan class constructor

   The constructor __init__ assigns book and member to instance variables.

2. Step 2: Check the print statement output

   Printing loan.book and loan.member outputs the strings '1984' and 'Alice' separated by space.

3. Final Answer:

   1984 Alice -> Option A

4. Quick Check:

   loan.book and loan.member print values [OK]

Hint: Print instance variables to see stored values [OK]

Common Mistakes:

• Expecting object memory address output
• Confusing variable names with strings
• Assuming error due to parameters

4. Identify the error in this Python class design snippet for the Librarian class:

class Librarian:
    def __init__(self, name):
        self.name = name
    def addBook(book):
        print(f"Adding {book} to library")

medium

A. Missing self parameter in addBook method

B. Incorrect print statement syntax

C. Constructor missing return statement

D. Class name should be lowercase

Solution

1. Step 1: Check method parameters in class

   Instance methods must include self as the first parameter to access instance data.

2. Step 2: Verify addBook method signature

   addBook lacks self, so it will cause an error when called on an instance.

3. Final Answer:

   Missing self parameter in addBook method -> Option A

4. Quick Check:

   Instance methods need self param [OK]

Hint: Instance methods always start with self parameter [OK]

Common Mistakes:

• Thinking print syntax is wrong
• Expecting constructor to return value
• Believing class names must be lowercase

5. In designing a library system, which class should handle the logic to check if a book is currently loaned out before allowing a member to borrow it?

hard

A. Book

B. Member

C. Loan

D. Librarian

Solution

1. Step 1: Understand responsibilities of each class

   Book stores book info, Member represents users, Loan tracks borrow records, and Librarian manages library operations.

2. Step 2: Identify who controls borrowing rules

   The Loan class should handle checking if a book is currently loaned out before allowing borrowing, as it tracks loan records.

3. Final Answer:

   Loan -> Option C

4. Quick Check:

   Loan class tracks loan status [OK]

Hint: Loan class tracks if a book is loaned out [OK]

Common Mistakes:

• Putting borrowing logic inside Book class
• Assigning loan status check to Member
• Expecting Librarian class to enforce borrowing rules