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PlantUML Language specification Use Case Diagram

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Use Case Diagram

A use case diagram is a visual representation used in software engineering to depict the interactions between system actors and the system itself. It captures the dynamic behavior of a system by illustrating its use cases and the roles that interact with them. These diagrams are essential in specifying the system's functional requirements and understanding how users will interact with the system. By providing a high-level view, use case diagrams help stakeholders understand the system's functionality and its potential value.

PlantUML offers a unique approach to creating use case diagrams through its text-based language. One of the primary advantages of using PlantUML is its simplicity and efficiency. Instead of manually drawing shapes and connections, users can define their diagrams using intuitive and concise textual descriptions. This not only speeds up the diagram creation process but also ensures consistency and accuracy. The ability to integrate with various documentation platforms and its wide range of supported output formats make PlantUML a versatile tool for both developers and non-developers. Lastly, being open-source, PlantUML boasts a strong community that continually contributes to its improvement and offers a wealth of resources for users at all levels.

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Usecases

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.

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@startuml

(First usecase)
(Another usecase) as (UC2)
usecase UC3
usecase (Last\nusecase) as UC4

@enduml

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Actors

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.

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@startuml

:First Actor:
:Another\nactor: as Man2
actor Woman3
actor :Last actor: as Person1

@enduml

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Change Actor style

You can change the actor style from stick man (by default) to:

Stick man (by default)

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@startuml
:User: --> (Use)
"Main Admin" as Admin
"Use the application" as (Use)
Admin --> (Admin the application)
@enduml

Awesome man

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@startuml
skinparam actorStyle awesome
:User: --> (Use)
"Main Admin" as Admin
"Use the application" as (Use)
Admin --> (Admin the application)
@enduml

[Ref. QA-10493]

Hollow man

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@startuml
skinparam actorStyle Hollow 
:User: --> (Use)
"Main Admin" as Admin
"Use the application" as (Use)
Admin --> (Admin the application)
@enduml

[Ref. PR#396]

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Usecases description

If you want to have a description spanning several lines, you can use quotes.

You can also use the following separators:

By using them pairwise and enclosing text between them, you can created separators with titles.

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@startuml

usecase UC1 as "You can use
several lines to define your usecase.
You can also use separators.
--
Several separators are possible.
==
And you can add titles:
..Conclusion..
This allows large description."

@enduml

Please note that the alias and the description are switched around from the basic example:

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@startuml
usecase description1 as alias1
usecase alias2 as "description2"
@enduml

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Use package

You can use packages to group actors or use cases.

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@startuml
left to right direction
actor Guest as g
package Professional {
  actor Chef as c
  actor "Food Critic" as fc
}
package Restaurant {
  usecase "Eat Food" as UC1
  usecase "Pay for Food" as UC2
  usecase "Drink" as UC3
  usecase "Review" as UC4
}
fc --> UC4
g --> UC1
g --> UC2
g --> UC3
@enduml

You can use rectangle to change the display of the package.

🎉 Copied! 

@startuml
left to right direction
actor "Food Critic" as fc
rectangle Restaurant {
  usecase "Eat Food" as UC1
  usecase "Pay for Food" as UC2
  usecase "Drink" as UC3
}
fc --> UC1
fc --> UC2
fc --> UC3
@enduml

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Basic example

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.

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@startuml

User -> (Start)
User --> (Use the application) : A small label

:Main Admin: ---> (Use the application) : This is\nyet another\nlabel

@enduml

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Extension

If one actor/use case extends another one, you can use the symbol <|--.

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@startuml
:Main Admin: as Admin
(Use the application) as (Use)

User <|-- Admin
(Start) <|-- (Use)

@enduml

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Using notes

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.

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@startuml
:Main Admin: as Admin
(Use the application) as (Use)

User -> (Start)
User --> (Use)

Admin ---> (Use)

note right of Admin : This is an example.

note right of (Use)
  A note can also
  be on several lines
end note

note "This note is connected\nto several objects." as N2
(Start) .. N2
N2 .. (Use)
@enduml

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Stereotypes

You can add stereotypes while defining actors and use cases using << and >>.

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@startuml
User << Human >>
:Main Database: as MySql << Application >>
(Start) << One Shot >>
(Use the application) as (Use) << Main >>

User -> (Start)
User --> (Use)

MySql --> (Use)

@enduml

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Changing arrows direction

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:

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@startuml
:user: --> (Use case 1)
:user: -> (Use case 2)
@enduml

You can also change directions by reversing the link:

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@startuml
(Use case 1) <.. :user:
(Use case 2) <- :user:
@enduml

It is also possible to change arrow direction by adding left, right, up or down keywords inside the arrow:

🎉 Copied! 

@startuml
:user: -left-> (dummyLeft)
:user: -right-> (dummyRight)
:user: -up-> (dummyUp)
:user: -down-> (dummyDown)
@enduml

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:

🎉 Copied! 

@startuml
left to right direction
:user: -left-> (dummyLeft)
:user: -right-> (dummyRight)
:user: -up-> (dummyUp)
:user: -down-> (dummyDown)
@enduml

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Splitting diagrams

The newpage keywords to split your diagram into several pages or images.

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@startuml
:actor1: --> (Usecase1)
newpage
:actor2: --> (Usecase2)
@enduml

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Left to right direction

The general default behavior when building diagram is top to bottom.

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@startuml
'default
top to bottom direction
user1 --> (Usecase 1)
user2 --> (Usecase 2)

@enduml

You may change to left to right using the left to right direction command. The result is often better with this direction.

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@startuml

left to right direction
user1 --> (Usecase 1)
user2 --> (Usecase 2)

@enduml

See also 'Change diagram orientation' on Deployment diagram page.

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Skinparam

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.

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@startuml
!option handwritten true

skinparam usecase {
BackgroundColor DarkSeaGreen
BorderColor DarkSlateGray

BackgroundColor<< Main >> YellowGreen
BorderColor<< Main >> YellowGreen

ArrowColor Olive
ActorBorderColor black
ActorFontName Courier

ActorBackgroundColor<< Human >> Gold
}

User << Human >>
:Main Database: as MySql << Application >>
(Start) << One Shot >>
(Use the application) as (Use) << Main >>

User -> (Start)
User --> (Use)

MySql --> (Use)

@enduml

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Complete example

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@startuml
left to right direction
skinparam packageStyle rectangle
actor customer
actor clerk
rectangle checkout {
  customer -- (checkout)
  (checkout) .> (payment) : include
  (help) .> (checkout) : extends
  (checkout) -- clerk
}
@enduml

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Business Use Case

You can add / to make Business Use Case.

Business Usecase

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@startuml

(First usecase)/
(Another usecase)/ as (UC2)
usecase/ UC3
usecase/ (Last\nusecase) as UC4

@enduml

Business Actor

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@startuml

:First Actor:/
:Another\nactor:/ as Man2
actor/ Woman3
actor/ :Last actor: as Person1

@enduml

[Ref. QA-12179]

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Change arrow color and style (inline style)

You can change the color or style of individual arrows using the inline following notation:

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@startuml
actor foo
foo --> (bar) : normal
foo --> (bar1) #line:red;line.bold;text:red  : red bold
foo --> (bar2) #green;line.dashed;text:green : green dashed 
foo --> (bar3) #blue;line.dotted;text:blue   : blue dotted
@enduml

[Ref. QA-3770 and QA-3816] [See similar feature on deployment-diagram or class diagram]

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Change element color and style (inline style)

You can change the color or style of individual element using the following notation:

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@startuml
actor a
actor b #pink;line:red;line.bold;text:red
usecase c #palegreen;line:green;line.dashed;text:green
usecase d #aliceblue;line:blue;line.dotted;text:blue
@enduml

[Ref. QA-5340 and adapted from QA-6852]

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Display JSON Data on Usecase diagram

Simple example

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@startuml
allowmixing

actor     Actor
usecase   Usecase

json JSON {
   "fruit":"Apple",
   "size":"Large",
   "color": ["Red", "Green"]
}
@enduml

[Ref. QA-15481]

For another example, see on JSON page.