UML Diagram Examples
This page provides an overview of each of the main types of UML diagrams, as well as relevant examples. UML is an acronym for the Unified Modeling Language, a standardized diagramming language used to describe numerous systems.
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Why Use UML?
UML was first implemented because software engineers needed a simple and consistent way to communicate in a field where programming languages develop at a rapid pace.
Today, UML offers that same simplicity and consistency to a variety of professionals, from engineers to business experts. You can use UML to capture a variety of complex processes, then communicate them to your colleagues.
When to Use UML
UML diagrams are frequently used to describe broad, high-level views of processes or relationships. Each type of UML diagram has individualized purposes, but overall, UML is well suited for:
- Planning system implementation and outlining system requirements.
- Illustrating system schematics with appropriate shapes.
- Creating and modifying detailed systems.
- Supplement planning and specification documentation.
UML Diagram Examples by Type
Outlined below are the main types of diagrams you might want to create. We also describe briefly how to use these diagrams and provide links to example pages for each type.
To make these diagrams, you'll need an assortment of symbols. You can find these symbols in the Lucidchart UML shape library. Once you start drawing, Lucidchart makes it easy to use correct notation, often prompting you with the next one automatically.
Use Case Diagrams
A use case diagram expresses how a user might use an object or system. In the diagram, the potential user is represented by a stick figure, called an “actor” symbol, and the various use cases are symbolized by oval shapes. Use case diagrams are ideal for communicating the principal functions of software systems, but they also have other valuable applications.
Activity diagrams are behavior-based flowcharts that capture processes from start to finish. Many UML diagrams generally describe software, but activity diagrams are often used to model other flows, such as showing how a patient checks into a hospital. If you need to take a closer look at a process, you’ll find activity diagrams helpful.
Class diagrams organize elements into objects and classes. They are structural diagrams that are useful for identifying relationships between objects and for categorizing objects in an accessible and coherent manner.
A sequence diagram shows how events occur in sequential order over the flow of time. Objects and actors in the sequence are depicted with several different symbols. As time passes, the objects send messages to each other via arrows. Sequence diagrams have several sub-types, timing diagrams and system sequence diagrams, that serve more individualized purposes, so click on the links if you'd like to learn more.
Component diagrams fall under the structural diagram category in UML. They depict how various components in a software system are wired together to form a total product. Component diagrams include several main shapes, including the rectangular component shape and the circular lollipop shape.
Deployment diagrams, another group of structural diagrams, describe not only the software of a system but the hardware as well. They get their name from showing which software elements are deployed by the hardware. Their main shape is a large three-dimensional box known as a node, which represents the object doing the deploying.
Object diagrams are related to class diagrams and look similar to them, using much of the same notation. They are more specific and concrete than class diagrams, however, because they depict particular instances of classes and their attributes, rather than the overall classes themselves.
State diagrams, also known as state machine diagrams, are a type of behavior diagram in UML. They illustrate how objects move from state to state via transition messages. The main shape for these is a rectangle with rounded corners.
With Lucidchart, creating professional-grade flowcharts has never been more simple. You will find the process completely intuitive; simply drag and drop any shape you want to build your diagram.