Write UML Diagrams using PlantUML

Why

We often need to use UML tools in our daily work. There are plenty of commercial or open source UML tools - List_UML_Tools. The reason that I would like to introduce you this PlantUML + Gravizo:

More lightweight and Open Source
UML diagrams are created via Diagrams are defined using a simple and intuitive language.
Friendly to version control system.

What is PlantUML

plantuml

To be able to generate some diagrams, you must have Graphviz software installed on your machine.

Graphviz is open source graph visualization software. Graph visualization is a way of representing structural information as diagrams of abstract graphs and networks. It has important applications in networking, bioinformatics, software engineering, database and web design, machine learning, and in visual interfaces for other technical domains.

Prerequisites

plantuml
graphviz
VS Code + plantuml(plugin) + markdown (Optional)

Note: Make sure plantuml command line is available

How to Show/Generate Diagrams

PlantUML command line

⇒  plantuml test_flow.wsd

You will find a png file generated

UML diagram in VS Code with markdown

```plantuml
@startuml
actor User
participant "First Class" as A
participant "Second Class" as B
participant "Last Class" as C

User -> A: DoWork
activate A

A -> B: Create Request
activate B

B -> C: DoWork
activate C

C --> B: WorkDone
destroy C

B --> A: Request Created
deactivate B

A --> User: Done
deactivate A
@enduml
```

Press Ctrl + K, V then a preview will be shown

PlantUML Web Server

http://www.plantuml.com/plantuml/uml/

Sequence Diagram

@startuml
participant User

User -> A: DoWork
activate A #FFBBBB

A -> A: Internal call
activate A #DarkSalmon

A -> B: << createRequest >>
activate B

B --> A: RequestCreated
deactivate B
deactivate A
A -> User: Done
deactivate A

@enduml

seq_diagram

Class Diagram

@startuml
class Car

Driver - Car : drives >
Car *- Wheel : have 4 >
Car -- Person : < owns

@enduml

class_diagram

Gantt Diagram

@startgantt
project starts the 2018/04/09
saturday are closed
sunday are closed
2018/05/01 is closed
2018/04/17 to 2018/04/19 is closed
[Prototype design] lasts 14 days
[Test prototype] lasts 4 days
[Test prototype] starts at [Prototype design]'s end
[Prototype design] is colored in Fuchsia/FireBrick 
[Test prototype] is colored in GreenYellow/Green 
@endgantt

gantt diagram

PlantUML supports more type of diagrams than that I mentioned above, it also supports Math diagram in latex but needs additional software (AsciiMath or JLaTeXMath).

@startuml
participant User

User -> A: DoWork
activate A #FFBBBB

A -> A: Internal call
activate A #DarkSalmon

A -> B: << createRequest >>
activate B

B --> A: RequestCreated
deactivate B
deactivate A
A -> User: Done
deactivate A

@enduml

Why