Unified Modeling Language (UML)

UML Definition

The Unified Modeling Language (UML) is a general-purpose, developmental, modeling language in the field of software engineering that is intended to provide a standard way to visualize the design of a system.

UML Tool

Create flowcharts & diagrams online with Lucidchart. No download needed. Use Lucidchart  to visualize ideas, make charts, diagrams & more.

UML Class Diagram

The UML Class diagram is a graphical notation used to construct and visualize object-oriented systems.

A class diagram in the Unified Modeling Language (UML) is a type of static structure diagram that describes the structure of a system:

  • classes
  • their attributes
  • operations (or methods)
  • and the relationships among objects


UML Class Notation

Class Access Modifiers

Perspectives of Class Diagram

The choice of perspective depends on how far you are in the development process. During the formulation of a domain model, for example, you would seldom move past the conceptual perspectiveAnalysis models will typically feature a mix of conceptual and specification perspectivesDesign model development will generally start with a heavy emphasis on specification and evolve into implementation perspectives.


  • Conceptual: represents the concepts in the domain
  • Specification: the focus is on the interfaces of Abstract Data Type (ADTs) in the software
  • Implementation: describes how classes will implement their interfaces.

Relationships between classes


Class Diagram Example