Use Case

The use_case is the meat of use case diagrams. It is a set of behaviors that will be performed by an actor or actors in the diagram.

Declaration

There are two methods for declaring a use_case. One method uses the command word usecase. The other method requires placing the name of the use case inside parentheses.

Example:

@startuml
'Example: Use Case Declaration

'Declare a use_case with the usecase command.
usecase Check

'Declare a use_case with parentheses.
(Stock)

@enduml

Properties

Use cases have eight properties. All are optional except description. The properties generally follow the below order.

• description - explains the action performed in the use case

• business - determines if the use case is a business use case

• alias - gives the ability to use a variable to identify the use case

• stereotype - applies a stereotype text to the use case

• fill_color - changes the interior color of the use case

• line_color - determines the color of the line used to draw the use case

• line_type - determines the type of line used to draw the use case

• text_color - determines the color of the description and stereotype text

The business property may come before or after description. The last four properties follow a hash (#) sign and are separated by a semicolon (;) if more than one is used. The last three properties can be in any order so long as they are the last three.

Description

The description is text that appears inside the use_case oval. The description can be a single word or it can be a string. Multiword strings must be inside parentheses. The string method supports line breaks as well as markup for color and emphasis. You can define colors with a standard color name or hex code.

Note: If color formatting is used inside of the description property it will override text_color. See Text Color for example.

Example: Use Case Description

@startuml
'Example: Use Case Description

'Declare a multline use_case with the usecase command.
usecase (Check\nCustomers)

'Declare a multiword use_case with parentheses.
'Use markup to add color and emphasis.
(<font color=561D5E><b>Stock Shelves</b></font>)

@enduml

Business

The business property is turned on by placing a forward slash after the usecase command or after the last parentheses around description.

Example Business Use Case

@startuml
'Example: Business Use Case

'Create a business use_case with the usecase command.
usecase/ Check

'Create a business use_case with parentheses.
(Stock)/

@enduml

Alias

The alias is exactly that. It is a variable that represents a use_case. It is especially useful if the use_case has a long description. The variable for the alias follows the as keyword.

There will be an actor and an association in the following example. This is needed to show the importance of the alias. They will not be explained here. See their respective sections of this chapter for proper explanations.

Notice how much easier it is to create an association with the Clock alias on line 15. Otherwise you must write the entire description as shown for Stock Shelves on line 18.

Example: Use Case Alias

@startuml
'Example: Use Case Alias

'Create an actor.
:Zarek:

'Create a use case and use markup for color and emphasis.
'Give the use case an alias.
(<font color=561D5E><b>Clock In</b></font>) as Clock

'Create a multiline use case.
(Stock\nShelves)

'Create an association between your actor and the first use case.
Zarek -- Clock

'Create an association between your actor and the second use case.
Zarek -- (Stock\nShelves)

@enduml

Stereotype

The stereotype field is defined by text between a double set of greater than and less than signs. This adds stereotype text above the description inside the oval icon. The stereotype text will be displayed in the color of the text_color property.

startuml
'Example: Use Case Stereotype

'Create a use_case with a stereotype.
usecase (Clock In) <<General Duty>> 

'Create another use_case with a stereotype.
(Bag Items) <<Cashier Duty>>

@enduml

Fill Color

The fill_color is defined by a standard color name or hex code. It determines the interior color of the actor icon. For the standard stick figure this is the interior of the head. If you use this property at all it must come immediately after a hash (#) sign and touch the hash sign. If any other properties follow this place a semicolon (;) between them. No spaces are needed.

Example: Use Case Fill Color

@startuml
'Example: Use Case Fill Color

'Create a use_case with a fill_color. 
usecase (Clock In) #red

'Create a use_case with a fill_color.
(Bag Items) #00FF00

@enduml

Line Color

The line_color is defined by a standard color name or hex code. It determines the color of the line that defines the outer edge of the use_case oval icon. If you use this property alone it must come after a hash (#) sign and touch the hash sign. If any other properties follow this place a semicolon (;) between them. No spaces are needed.

Example: Use Case Line Color

@startuml
'Example: Use Case Line Color

'Create a use_case with a line_color. 
usecase (Clock In) #line:red

'Create a use_case with a line_color.
(Bag Items) #line:00FF00

@enduml

Line Type

The line_type defines the texture of the exterior line of the use_case icon. If you use this property alone it must come after a hash (#) sign and touch the hash sign. If any other properties follow this place a semicolon (;) between them. No spaces are needed.

The line_types are as follows.

• line.bold

• line.dashed

• line.dotted

Example: Use Case Line Type

@startuml
'Example: Use Case Line Type

'Create a use_case with a bold line.
usecase (Clock In) #line.bold

'Create a use_case with a dashed line.
(Bag Items) #line.dashed

'Create a use_case with a dotted line.
(Mop Floors) #line.dotted

@enduml

Text Color

The text_color is defined by a standard color name or hex code. It determines the color of the description and the stereotype. If you use this property alone it must come after a hash (#) sign and touch the hash sign. If any other properties follow this place a semicolon (;) between them. No spaces are needed.

Note: If color formatting is used inside of the description property it will override text_color.

Example: Use Case Text Color

@startuml
'Example: Use Case Text Color

'Create a use_case with a text_color.
'Assign a stereotype.
usecase (Clock In) <<General Duty>> #text:red

'Create a use_case and use markup for description color.
'Change the text_color to a different color than the description.
'Assign a stereotype.
(<font color=561D5E>Bag Items</font>) <<Cashier Duty>> #text:00FF00

@enduml

With All Properties

Example: Use Case With All Properties

@startuml
'Example: Use Case With All Properties

'Create a use_case with all properties with parentheses.
(<font color=FFFFFF>Bag Items</font>)/ as bag <<Cashier Duty>> #561D5E;line:blue;line.bold;text:B0B0B0;

'Create a use_case with all properties with the usecase command.
usecase/ (<font color=FFFFFF>Stock Shelves</font>) as stock <<Cashier Duty>> #561D5E;line:blue;line.bold;text:B0B0B0;

@enduml

Special Description

You can use multiple lines to create a very descriptive use_case. For this we will swap the order of the description and alias properties. The description can take up several lines but must be inside of quotation marks. Special description supports markup for color and emphasis. You can define colors with a standard color name or hex code.

One other feature of the special description is that it supports visual separators. The separators can stand alone by placing two of the separator characters on a line. Or the visual separator can encompass text by wrapping the text in two sets of two characters. The four types of separators are shown below.

• -- - creates a dashed separating line

• .. - creates a dotted separating line

• == - creates a double lines separator

• _ _ - creates a solid line separator

Note: Vertical empty space inside the special description will appear in the diagram. See lines 13 and 15.

Note: Special Description does not support any other use_case properties.

Example: Use Case Special Description

@startuml
'Example: Use Case Special Description

'Create a use_case with a special description.
'Make it a multiline description with mixed and matched separators.
'Use markup to color and emphasize text.
usecase Mop as "
Mop Floors
__
Fill Bucket
With Water
==

..Add Cleaning Solution...

--
<font color=561D5E><i>Place Mop Head</i></font>
In Bucket
"

@enduml