Library Management System

Library Management System - Class Diagram

This class diagram illustrates a comprehensive library management system, demonstrating advanced object-oriented design principles including inheritance, abstract classes, association classes, and complex relationships between various entities in a modern library environment.

Core Abstract Classes:

LibraryItem (Abstract Base Class)

Purpose: Represents any item that can be borrowed from the library Key Attributes:

• id: Unique identifier for each library item
• title: Title of the item (book, DVD, magazine, etc.)
• isbn: International Standard identifier
• publishedDate: Publication or release date
• publisher: Publishing company or distributor
• status: Current availability status (available, checked out, reserved, etc.)
• location: Physical location within the library

Key Methods:

• isAvailable(): Checks if item can be borrowed
• updateStatus(): Changes item availability status
• calculateLateFee(): Abstract method for late fee calculation (varies by item type)
• getMaxLoanPeriod(): Abstract method for maximum borrowing period

Person (Abstract Base Class)

Purpose: Base class for all people interacting with the library system Key Attributes:

• id: Unique person identifier
• firstName, lastName: Personal identification
• email, phoneNumber: Contact information
• address: Physical address (composition relationship)

Key Methods:

• getFullName(): Concatenates first and last names
• updateContactInfo(): Updates email and phone
• getMaxBorrowLimit(): Abstract method (varies by person type)

Concrete Item Classes:

Book Class

Inheritance: Extends LibraryItem Specific Attributes:

• author: Book author(s)
• genre: Literary classification (fiction, non-fiction, science, etc.)
• pageCount: Number of pages
• language: Language of publication

Specialized Behavior:

• calculateLateFee(): Books have standard late fee structure
• getMaxLoanPeriod(): Typically 21 days for books

DVD Class

Inheritance: Extends LibraryItem Specific Attributes:

• director: Film or content director
• duration: Runtime in minutes
• rating: Content rating (G, PG, R, etc.)
• format: Physical format (DVD, Blu-ray, 4K)

Specialized Behavior:

• calculateLateFee(): DVDs often have higher late fees
• getMaxLoanPeriod(): Typically 7 days for DVDs

Magazine Class

Inheritance: Extends LibraryItem Specific Attributes:

• issueNumber: Specific issue identifier
• volume: Volume number
• frequency: Publication frequency (weekly, monthly, quarterly)

Specialized Behavior:

• getIssueInfo(): Formats volume and issue information
• calculateLateFee(): Magazines may have minimal or no late fees
• getMaxLoanPeriod(): Typically 14 days for magazines

Person Subclasses:

Member Class

Inheritance: Extends Person Specific Attributes:

• membershipType: Type of membership (student, faculty, community, premium)
• membershipDate: When membership began
• fines: Current outstanding fines
• borrowingHistory: Complete history of loans

Key Methods:

• getMembershipType(): Returns membership classification
• payFine(): Processes fine payment
• getMaxBorrowLimit(): Varies by membership type (students: 5, faculty: 10, etc.)
• canBorrow(): Checks if member is eligible to borrow (no excessive fines, under limit)

Librarian Class

Inheritance: Extends Person Specific Attributes:

• employeeId: Staff identification number
• department: Working department (circulation, reference, technical services)
• permissions: Set of system permissions for different operations

Key Methods:

• processLoan(): Creates new loan record
• processReturn(): Handles item returns and calculates fees
• addNewItem(): Adds items to library catalog
• getMaxBorrowLimit(): Librarians typically have higher limits for professional needs

Association and Supporting Classes:

Loan Class (Association Class)

Purpose: Represents the borrowing relationship between Member and LibraryItem Key Attributes:

• loanId: Unique loan identifier
• loanDate: When item was borrowed
• dueDate: When item must be returned
• returnDate: Actual return date (null if still out)
• renewalCount: Number of times loan has been renewed
• lateFee: Calculated late fee amount

Key Methods:

• isOverdue(): Checks if current date exceeds due date
• calculateLateFee(): Computes fees based on days overdue and item type
• renew(): Extends due date if renewal is allowed
• markReturned(): Records return date and finalizes loan

Reservation Class

Purpose: Manages holds placed on currently unavailable items Key Attributes:

• reservationId: Unique reservation identifier
• reservationDate: When reservation was placed
• expiryDate: When reservation expires if not fulfilled
• priority: Queue position for popular items

Key Methods:

• isActive(): Checks if reservation is still valid
• cancel(): Removes reservation from queue
• fulfill(): Converts reservation to loan when item becomes available

System Management Classes:

Library Class

Purpose: Main system coordinator and entry point Key Attributes:

• name: Library name and identification
• address: Physical library location
• phoneNumber: Contact information
• openingHours: Operating schedule by day of week
• catalog: Reference to the item catalog

Key Methods:

• searchItems(): Searches across all library items
• registerMember(): Creates new member accounts
• processLoan(): Coordinates borrowing process

Catalog Class

Purpose: Manages the complete collection of library items Key Attributes:

• items: Map of all library items indexed by ID

Key Methods:

• addItem(): Adds new items to collection
• removeItem(): Removes items from collection
• searchByTitle(): Title-based search functionality
• searchByAuthor(): Author-based search for books
• getAvailableItems(): Returns only currently available items

Enumerations and Value Objects:

ItemStatus Enumeration

Values: AVAILABLE, CHECKED_OUT, RESERVED, DAMAGED, LOST, UNDER_REPAIR Purpose: Standardizes item availability states across the system

MembershipType Enumeration

Values: STUDENT, FACULTY, COMMUNITY, PREMIUM Purpose: Defines different membership categories with varying privileges

Permission Enumeration

Values: ADD_ITEM, REMOVE_ITEM, MANAGE_MEMBERS, OVERRIDE_LIMITS, GENERATE_REPORTS Purpose: Controls librarian access to different system functions

Address Class (Value Object)

Purpose: Encapsulates complete address information Attributes: street, city, state, zipCode, country Behavior: Provides formatted address string

Money Class (Value Object)

Purpose: Handles monetary calculations with precision Attributes: amount (BigDecimal), currency Behavior: Mathematical operations (add, subtract), zero checking

Relationship Patterns and Design Principles:

Inheritance Hierarchies:

• LibraryItem Hierarchy: Demonstrates polymorphism where different item types implement abstract methods differently
• Person Hierarchy: Shows how different user roles extend common person functionality

Association Classes:

• Loan Class: Perfect example of association class representing the many-to-many relationship between Members and LibraryItems with additional attributes

Composition vs Aggregation:

• Composition: Library contains Catalog (strong ownership)
• Aggregation: Person has Address (shared relationship)

Advanced OOP Concepts Demonstrated:

Abstract Classes and Methods:

• LibraryItem: Defines common interface while allowing specialized implementations
• Person: Provides shared functionality while requiring subclass-specific behavior

Polymorphism:

• calculateLateFee(): Each item type implements its own fee structure
• getMaxLoanPeriod(): Different loan periods for different item types
• getMaxBorrowLimit(): Varies by person type (member vs librarian)

Encapsulation:

• Protected fields in abstract classes allow subclass access while maintaining encapsulation
• Private fields in concrete classes ensure proper data hiding

Method Overriding:

• Subclasses override abstract methods to provide type-specific behavior
• Template method pattern in base classes defines algorithm structure

Business Rules and Constraints:

Borrowing Rules:

• Members must be in good standing (no excessive fines) to borrow
• Different membership types have different borrowing limits
• Item-specific loan periods and renewal policies
• Late fees calculated based on item type and overdue duration

Inventory Management:

• Items tracked through complete lifecycle (available → borrowed → returned)
• Reservation system manages demand for popular items
• Status tracking for damaged or lost items

Access Control:

• Librarian permissions control system access
• Different staff roles have different capabilities
• Member privacy and data protection considerations

Technical Implementation Considerations:

Database Mapping:

• Abstract classes map to table-per-class or table-per-hierarchy strategies
• Association classes require junction tables with additional attributes
• Enumeration values stored as strings or integers with validation

Search and Indexing:

• Catalog search functionality requires efficient indexing
• Full-text search capabilities for titles, authors, and descriptions
• Category and genre-based browsing support

Scalability Features:

• Catalog design supports large collections
• Loan history maintained for analytics and reporting
• Reservation queue management for high-demand items

Integration Points:

• External library systems (interlibrary loans)
• Payment processing for fines and fees
• Digital content management for e-books and streaming
• Inventory management systems for acquisitions

This class diagram effectively demonstrates sophisticated object-oriented design principles while modeling a real-world system that balances complexity with maintainability, showing how inheritance, polymorphism, and association classes work together to create a flexible and extensible library management solution.