Class Diagram - Unified Modeling Language (UML)

Overview

• A UML class diagram is a visual tool to represent the structure of a system, showcasing classes, attributes, methods, and relationships.
• Utilized in software engineering to facilitate understanding among developers and designers of how a system is organized and its components interact.

What are Class Diagrams?

• A type of UML diagram for visually representing the structure and relationships of classes within a system.
• Depicts classes as boxes with compartments for class name, attributes, and methods.
• Lines between classes illustrate associations and relationships such as one-to-one or one-to-many.

What is a Class?

• In OOP, a class is a blueprint for creating objects, defining a set of attributes and methods.
• Attributes represent the object's characteristics; methods define behaviors.

UML Class Notation

• Class Name: Centered and bold in the top compartment of the class box.
• Attributes: Properties or fields listed with visibility and data type in the second compartment.
• Methods: Functions or operations with visibility, return type, and parameters in the third compartment.
• Visibility Notation:
  • + (public), - (private), # (protected), ~ (package/default)

Parameter Directionality

• In (Input): Arrow towards the receiving class.
• Out (Output): Arrow away from the receiving class.
• InOut (Input and Output): Arrows pointing both towards and away from the receiving class.

Relationships between Classes

Association

• Bi-directional relationship between two classes, depicted by a solid line.

Directed Association

• Relationship with a direction, indicated by an arrowhead.

Aggregation

• Whole-part relationship where the part can exist independently.

Composition

• Stronger form of aggregation where the part cannot exist independently.

Generalization (Inheritance)

• "Is-a" relationship where a subclass inherits from a superclass.

Realization (Interface Implementation)

• Class implements the features of an interface, depicted by a dashed line with an open arrowhead.

Dependency

• One class relies on another but is more loosely coupled than association or inheritance.

Usage (Dependency) Relationship

• Indicates that one class utilizes or depends on another class.

Purpose of Class Diagrams

• Depict various aspects of the OOP concept.
• Facilitate faster and more efficient application design and analysis.
• Form the base for deployment and component diagrams.
• Support forward and reverse engineering.

Benefits of Class Diagrams

• Provide a clear view of system architecture.
• Show relationships between classes, aiding in understanding component connectivity.
• Serve as a communication tool among team members and stakeholders.
• Guide developers in coding, ensuring design consistency with implementation.
• Enable code generation, reducing manual errors and saving time.

How to Draw Class Diagrams

1. Identify Classes: Determine the classes in the system.
2. List Attributes and Methods: Document attributes and methods for each class.
3. Identify Relationships: Determine relationships like associations and dependencies.
4. Create Class Boxes: Draw a rectangle for each class.
5. Add Attributes and Methods: List attributes and methods with visibility notations.
6. Draw Relationships: Use lines and arrows to represent relationships.
7. Label Relationships: Indicate multiplicity and role names.
8. Review and Refine: Ensure accuracy and refine based on feedback.

Use Cases of Class Diagrams

• Show the static structure of a software system.
• Help visualize and organize system components.
• Facilitate design discussions and shared understanding.
• Support code generation to create code skeletons efficiently.
• Minimize manual coding efforts and align implementation with design.