Components of a Class Diagram (Classes, Attributes, Operations)
Relationships in Class Diagrams (Association, Generalization, Aggregation, Composition)
Example: Library Management System Class Diagram
Advantages of Class Diagrams
Key Takeaways
Recap of Use Case Diagrams
Use Case Diagrams describe the functionality of a system from the user's perspective, showing actors and the use cases they perform. They are excellent for defining system scope and communicating with stakeholders.
What is a Class Diagram?
A Class Diagram is a structural UML diagram that describes the static structure of a system by showing the system's classes, their attributes, operations (or methods), and the relationships among objects.
It is the most common diagram in object-oriented modeling and is used for conceptual modeling of the system's structure.
Components of a Class Diagram: Classes
A class is a blueprint for creating objects (a particular data structure), providing initial values for state (member variables or attributes), and implementations of behavior (member functions or methods).
classDiagram
class ClassName {
+attribute1: Type
-attribute2: Type
+operation1()
-operation2()
}
Class Name: The name of the class.
Attributes: The properties or data fields of the class. (e.g., +name: String, -balance: Double)
Operations (Methods): The functions or behaviors that the class can perform. (e.g., +deposit(amount: Double))
Relationships in Class Diagrams: Association
An Association represents a relationship between two or more classes. It shows that objects of one class are connected to objects of another class.
classDiagram
Customer "1" -- "*" Order
Multiplicity: Indicates how many instances of one class are related to instances of another class (e.g., 1, *, 0..1, 1..*).
Navigability: Indicates the direction of the relationship (e.g., one-way or two-way).
Relationships in Class Diagrams: Generalization
Generalization represents an inheritance relationship, where a subclass inherits properties and behaviors from a superclass. It is an "is-a" relationship.
classDiagram
Animal <|-- Dog
Animal <|-- Cat
Dog is an Animal, Cat is an Animal.
Relationships in Class Diagrams: Aggregation & Composition
Both represent a "has-a" relationship, but with different strengths of ownership.
Aggregation (Weak "has-a"): Represents a whole-part relationship where the parts can exist independently of the whole. (Hollow diamond)
Composition (Strong "has-a"): Represents a whole-part relationship where the parts cannot exist independently of the whole. If the whole is destroyed, the parts are also destroyed. (Solid diamond)
classDiagram
Car o-- Wheel : Aggregation
House *-- Room : Composition
Example: Library Management System Class Diagram
classDiagram
class Library {
+name: String
+address: String
+addBook()
+removeBook()
+searchBook()
}
class Book {
+bookId: String
+title: String
+author: String
+ISBN: String
+isAvailable: Boolean
+getDetails()
}
class Member {
+memberId: String
+name: String
+email: String
+phone: String
+issueBook()
+returnBook()
}
class Transaction {
+transactionId: String
+issueDate: Date
+returnDate: Date
+fine: Double
+calculateFine()
}
Library "1" o-- "many" Book
Member "1" o-- "many" Transaction
Book "1" o-- "many" Transaction
Advantages of Class Diagrams
Visual Representation: Provides a clear, static view of the system's structure.
Detailed Design: Helps in designing the database schema and object-oriented code.
Communication: Facilitates communication among developers and stakeholders about the system's components.
Maintainability: A well-designed class diagram makes the system easier to understand and maintain.
Reusability: Promotes the identification of reusable components.
Key Takeaways
**Class Diagrams** show the static structure of a system.
They consist of **classes, attributes, and operations**.
Key relationships include **association, generalization, aggregation, and composition**.
They are essential for **object-oriented design** and **database modeling**.