UML Diagrams and Models

UML (Unified Modeling Language) is a standardized modeling language used to visually represent the design and structure of a system. In Object-Oriented Programming (OOP), UML diagrams help to model the relationships, interactions, and behavior of objects within a system. There are various types of UML diagrams that serve different purposes, such as Class Diagrams, Sequence Diagrams, Use Case Diagrams, and others.

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Types of UML Diagrams

Diagram Type	Description	Purpose
Class Diagram	Describes the static structure of a system by showing its classes, their attributes, methods, and relationships.	System structure
Object Diagram	Shows a snapshot of instances of classes at a particular moment in time.	Object state
Use Case Diagram	Represents the functional requirements of a system, showing actors and use cases.	Requirement analysis
Sequence Diagram	Describes how objects interact in a particular sequence, showing messages exchanged between objects.	Interaction behavior
Activity Diagram	Represents the workflow of a system or a process, illustrating the flow of control between activities.	Workflow modeling
State Diagram	Shows the states of an object and the transitions between those states.	State transitions
Component Diagram	Illustrates how components (like classes, modules, or libraries) are organized and interact.	System architecture
Deployment Diagram	Describes the physical deployment of artifacts (e.g., software and hardware) in a system.	Hardware/software architecture

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1. Class Diagram

Definition:

A Class Diagram shows the static structure of a system by displaying its classes, their attributes, methods, and relationships. It is one of the most commonly used diagrams in object-oriented design.

Key Elements:

• Classes: Represented by rectangles with three sections (name, attributes, and methods).
• Attributes: Represent the properties or data members of the class.
• Methods: Represent the operations or behaviors the class can perform.
• Relationships:
  • Association: A relationship where one class uses or interacts with another (e.g., aggregation, composition).
  • Inheritance (Generalization): A relationship where one class (subclass) inherits properties and behaviors from another (superclass).
  • Dependency: A relationship where one class depends on another.
  • Aggregation: A special form of association, representing a "whole-part" relationship where the part can exist independently.
  • Composition: A stronger form of aggregation where the part cannot exist without the whole.

Example of a Class Diagram

+-------------------+           +---------------------+
|      Person       |<>---------|       Address       |
+-------------------+           +---------------------+
| - name: string    |           | - street: string    |
| - age: int        |           | - city: string      |
+-------------------+           +---------------------+
| + getName(): string |         | + getFullAddress(): string |
+-------------------+           +---------------------+