UML Class Diagram with Example

What is a Class Diagram?

A class diagram is a visual representation in Unified Modeling Language (UML) that illustrates a system’s classes, attributes, methods, and relationships, providing an overview of its object-oriented structure.

UML Class Diagram Rules:

Class diagrams in UML follow certain rules and conventions to ensure clarity and accuracy in representing the structure and relationships within a system. There are some rules for making this diagram. Below is an attempt to provide these important rules:

1. A class is represented as a rectangle divided into three compartments. The class name is presented in the upper compartment. Attributes are kept in the middle compartment. Then methods are kept in the bottom compartment.
2. The convention is to present features in the middle compartment of the class rectangle. Each attribute must include its visibility. Then include the name of the attribute and its data type.
3. Procedures are to be presented in the box below the square rectangle. Every method has to include its visibility. Then include the method name, a parameter list in parentheses, and the return type.
4. Associations are depicted as lines connecting participating classes. A multiplicity index can be added to show how many instances belong to each class. The direction of the association arrow indicates the novelty of the relationship.
5. Aggregation represents a “whole-part” relationship, while composition indicates a stronger form of aggregation where the parts are closely tied to the whole. Diamond-shaped arrows are used to denote these relationships.
6. Inheritance is represented by an arrow with an open triangle pointing from the subclass (derived class) to the superclass (base class).
7. Interfaces are depicted similarly to classes. But with a stereotype “«interface»” placed above the name compartment. They define a contract of methods. That implementing classes must provide.
8. Italicized names denote abstract classes. They cannot be instantiated. Subclasses must implement the abstract methods.
9. Visibility indicators specify the access level of properties and methods (public, private, protected, package). Public members are protected with a “+”, private with a “-“, and a “#”. Then package-private is indicated with a “~”.
10. A dependency indicates that one class relies on another class. But there’s no significant relationship. A dashed arrow points from the dependent class to the class it depends on.

Class Diagram Example:

Uses of Class Diagram:

Class diagrams are used in software engineering to depict the static structure of a system or application. They are primarily associated with object-oriented programming and design. They help developers and designers communicate and visualize the relationships between classes, their attributes, methods, and associations. Class diagrams are used in various types of projects, including:

1. UML Modeling
2. Database Design
3. Software Development Projects
4. Object-Oriented Analysis and Design
5. Software Reengineering
6. Education and Training, Etc…

You can use UML diagrams in various areas of software engineering. Moreover, this diagram can be used for various business purposes. For example:

1. Business Process Modeling
2. Organizational Structure
3. Service-Oriented Architecture (SOA)
4. Business Rules and Logic
5. Communication and Collaboration

You can easily create a diagram using draw.io. Thank you for staying with us. For any suggestions or any type of tech-related help, you can contact us.