Syntax

->> 同步消息，-)异步消息。

sequenceDiagram
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!
    Alice-)John: See you later!

  sequenceDiagram
    Alice->>John: Hello John, how are you?
    John-->>Alice: Great!
    Alice-)John: See you later!

Participants

sequenceDiagram
    participant Alice
    participant Bob
    Bob->>Alice: Hi Alice
    Alice->>Bob: Hi Bob

  sequenceDiagram
    participant Alice
    participant Bob
    Bob->>Alice: Hi Alice
    Alice->>Bob: Hi Bob

Actors

actor 会有一个人物的标志。

sequenceDiagram
    actor Alice
    actor Bob
    Alice->>Bob: Hi Bob
    Bob->>Alice: Hi Alice

  sequenceDiagram
    actor Alice
    actor Bob
    Alice->>Bob: Hi Bob
    Bob->>Alice: Hi Alice

Aliases

sequenceDiagram
    participant A as Alice
    participant J as John
    A->>J: Hello John, how are you?
    J->>A: Great!

  sequenceDiagram
    participant A as Alice
    participant J as John
    A->>J: Hello John, how are you?
    J->>A: Great!

Grouping / Box

Messages

Activations

sequenceDiagram
    Alice->>John: Hello John, how are you?
    activate John
    John-->>Alice: Great!
    deactivate John

# 简化方式
sequenceDiagram
    Alice->>+John: Hello John, how are you?
    John-->>-Alice: Great!

  sequenceDiagram
    Alice->>+John: Hello John, how are you?
    John-->>-Alice: Great!

还可以 stack 起来：

sequenceDiagram
    Alice->>+John: Hello John, how are you?
    Alice->>+John: John, can you hear me?
    John-->>-Alice: Hi Alice, I can hear you!
    John-->>-Alice: I feel great!

  sequenceDiagram
    Alice->>+John: Hello John, how are you?
    Alice->>+John: John, can you hear me?
    John-->>-Alice: Hi Alice, I can hear you!
    John-->>-Alice: I feel great!

Notes

sequenceDiagram
    participant John
    Note right of John: Text in note

  sequenceDiagram
    participant John
    Note right of John: Text in note

还可以 Note over Alice,John: A typical interaction

Loops

loop Loop text
... statements ...
end

  sequenceDiagram
    Alice->John: Hello John, how are you?
    loop Every minute
        John-->Alice: Great!
    end

Alt

# if else
alt Describing text
... statements ...
else
... statements ...
end

# if
opt Describing text
... statements ...
end

  sequenceDiagram
    Alice->>Bob: Hello Bob, how are you?
    alt is sick
        Bob->>Alice: Not so good :(
    else is well
        Bob->>Alice: Feeling fresh like a daisy
    end
    opt Extra response
        Bob->>Alice: Thanks for asking
    end

Parallel

par [Action 1]
... statements ...
and [Action 2]
... statements ...
and [Action N]
... statements ...
end

  sequenceDiagram
    par Alice to Bob
        Alice->>Bob: Hello guys!
    and Alice to John
        Alice->>John: Hello guys!
    end
    Bob-->>Alice: Hi Alice!
    John-->>Alice: Hi Alice!

Critical Region

必须要执行的一段区域。

critical [Action that must be performed]
... statements ...
option [Circumstance A]
... statements ...
option [Circumstance B]
... statements ...
end

Break

break [something happened]
... statements ...
end

Background Highlight

rect COLOR
... content ...
end

rect rgb(0, 255, 0)
... content ...
end

rect rgba(0, 0, 255, .1)
... content ...
end

Comments

sequenceDiagram
    Alice->>John: Hello John, how are you?
    %% this is a comment
    John-->>Alice: Great!

sequenceNumbers

sequenceDiagram
    autonumber