A use case diagram shows how external actors interact with a system: who does what, and which features the system exposes. It's a high-level view of functional requirements, useful early in design to align stakeholders.
In PlantUML, you describe actors and use cases in text, and the connections between them. The diagram is generated for you.
- Text in, diagram out. Define actors, use cases, and links in a few lines.
- Easy to refactor. Rename an actor or move a use case by editing one line.
- Fits in your repo. Diagrams live next to the code they document, in version control.
See common commands for features available across all diagram types.
Use cases are enclosed using between parentheses (because two
parentheses looks like an oval).
You can also use the usecase keyword to define a
usecase.
And you can define an alias, using the as keyword.
This alias will be used later, when defining relations.
The name defining an actor is enclosed between colons.
You can also use the actor keyword to define an actor.
An alias can be assigned using the as keyword and can be used later instead of the actor's name, e. g. when defining relations.
You can see from the following examples, that the actor definitions are optional.
You can change the actor style from stick man (by default) to:
- an awesome man with the
skinparam actorStyle awesome command;
- a hollow man with the
skinparam actorStyle hollow command.
Stick man (by default)
Awesome man
[Ref. QA-10493]
Hollow man
[Ref. PR#396]
If you want to have a description spanning several lines, you can use quotes.
You can also use the following separators:
-- (dashes).. (periods)== (equals)__ (underscores)
By using them pairwise and enclosing text between them, you can created separators with titles.
Please note that the alias and the description are switched around from the basic example:
You can use packages to group actors or use cases.
You can use rectangle to change the display of the package.
To link actors and use cases, the arrow --> is
used.
The more dashes - in the arrow, the longer the
arrow.
You can add a label on the arrow, by adding a :
character in the arrow definition.
In this example, you see that User has not been defined
before, and is used as an actor.
If one actor/use case extends another one, you can use the symbol <|--.
You can use the note left of , note right of ,
note top of , note bottom of keywords to
define notes related to a single object.
A note can be also define alone with the note
keywords, then linked to other objects using the .. symbol.
You can add stereotypes while defining actors and use cases using << and >>.
By default, links between classes have two dashes -- and are vertically oriented.
It is possible to use horizontal link by putting a single dash (or dot) like this:
You can also change directions by reversing the link:
It is also possible to change arrow direction by adding left, right, up
or down keywords inside the arrow:
You can shorten the arrow by using only the first character of the direction (for example, -d- instead of
-down-)
or the two first characters (-do-).
Please note that you should not abuse this functionality : Graphviz gives usually good results without
tweaking.
And with the left to right direction parameter:
The newpage keywords to split your diagram into several pages or images.
The general default behavior when building diagram is top to bottom.
You may change to left to right using the left to right direction command.
The result is often better with this direction.
See also 'Change diagram orientation' on Deployment diagram page.
You can use the skinparam
command to change colors and fonts for the drawing.
You can use this command :
You can define specific color and fonts for stereotyped actors and usecases.
You can add / to make Business Use Case.
Business Usecase
Business Actor
[Ref. QA-12179]
You can change the color or style of individual arrows using the inline following notation:
#color;line.[bold|dashed|dotted];text:color
[Ref. QA-3770 and QA-3816]
[See similar feature on deployment-diagram or class diagram]
You can change the color or style of individual element using the following notation:
#[color|back:color];line:color;line.[bold|dashed|dotted];text:color
[Ref. QA-5340 and adapted from QA-6852]
Simple example
[Ref. QA-15481]
For another example, see on JSON page.
Usecases