======Use Case Diagram======
To be able to generate those diagrams, you must have Graphviz_software
installed on your machine in the default directory c:\Program
Files\GraphvizX.XX or /usr/bin/dot.
You can have_a_look_here_if_you_have_installed_Graphviz_somewhere_else.
Let's have a fews examples :
Note that you can disable the shadowing using the skinparam shadowing false
command.
======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 latter, when defining
relations.
<uml t="usecase">

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

</uml>
		
======Actors======
Actor are enclosed using between two points.
You can also use the actor keyword to define an actor. And you can define an
alias, using the as keyword. This alias will be used latter, when defining
relations.
We will see later that the actor definitions are optional.
<uml t="usecase_001">

:First Actor:
:Another\nactor: as Men2
actor Men3
actor :Last actor: as Men4

</uml>
		
======Usecases description======
If you want to have description on several lines, you can use quotes.
You can also use the following separators: -- .. == __. And you can put titles
within the separators.
<uml t="usecase_002">

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."

</uml>
		
======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.
<uml t="usecase_003">

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

:Main Admin: ---> (Use the application) : This is\nyet another\nlabel
</uml>
		
======Extension======
If one actor/use case extends another one, you can use the symbol <|-- (which
stands for [img/extends01.png]).
<uml t="usecase_004">
:Main Admin: as Admin
(Use the application) as (Use)

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

</uml>
		
======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.
@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)
</uml>
		
[imgp/usecase_005.png]
======Stereotypes======
You can add stereotypes while defining actors and use cases using " << " and "
>> ".
<uml t="usecase_006">
User << Human >>
:Main Database: as MySql << Application >>
(Start) << One Shot >>
(Use the application) as (Use) << Main >>

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

MySql --> (Use)

</uml>
		
======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:
<uml t="usecase_007">
:user: --> (Use case 1)
:user: -> (Use case 2)
</uml>
You can also change directions by reversing the link:
<uml t="usecase_008">
(Use case 1) <.. :user:
(Use case 2) <- :user:
</uml>
It is also possible to change arrow direction by adding left, right, up or down
keywords inside the arrow:
<uml t="usecase_009">
:user: -left-> (dummyLeft)
:user: -right-> (dummyRight)
:user: -up-> (dummyUp)
:user: -down-> (dummyDown)
</uml>
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.
======Title the diagram======
The title keywords is used to put a title.
You can use title and end title keywords for a longer title, as in sequence
diagrams.
<uml t="usecase_010">
title Simple <b>Usecase</b>\nwith one actor

"Use the application" as (Use)
User -> (Use)

</uml>
======Splitting diagrams======
The newpage keywords to split your diagram into several pages or images.
<uml t="usecase_011_001">
:actor1: --> (Usecase1)
newpage
:actor2: --> (Usecase2)
</uml>
======Left to right direction======
The general default behavior when building diagram is top to bottom.
<uml t="usecase_012">
'default
top to bottom direction
user1 --> (Usecase 1)
user2 --> (Usecase 2)

</uml>
You may change to left to right using the left to right direction command. The
result is often better with this direction.
<uml t="usecase_013">

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

</uml>
======Skinparam======
You can use the skinparam command to change colors and fonts for the drawing.
You can use this command :
    * In the diagram definition, like any other commands,
    * In an included_file,
    * In a configuration file, provided in the command_line or the ANT_task.
You can define specific color and fonts for stereotyped actors and usecases.
<uml t="usecase_014">

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)

</uml>
		
======Complete example======
<uml t="usecase_015">
left to right direction
skinparam packageStyle rect
actor customer
actor clerk
rectangle checkout {
  customer -- (checkout)
  (checkout) .> (payment) : include
  (help) .> (checkout) : extends
  (checkout) -- clerk
}
</uml>