A Sequence diagram is an interaction diagram that shows how processes operate with one another and in what order.
2.1 Participants
The participants or actors are rendered in order of appearance in the diagram source text.
Feature
Diagram
You can specify the actor's order of appearance to
show the participants in a different order.
sequenceDiagram
participant Alice
participant John
Alice->>John: John, how are you?
John-->>Alice: Great!
You can specify the actor’s order of appearance
to show the participants in a different order.
sequenceDiagram
Alice->>John: John, how are you?
John-->>Alice: Great!
The participants can be defined implicitly without
specifying them with the `participant` keyword.
sequenceDiagram
Alice->>John: John, how are you?
John-->>Alice: Great!
2.2 Aliases
The participant can have a convenient identifier and a descriptive label.
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!
2.3 Messages
Messages can be of two displayed either solid or with a dotted line.
[Actor][Arrow][Actor]:Message text
There are six types of arrows currently supported:
Arrow Type
Description
->
Solid line without arrow
-->
Dotted line without arrow
->>
Solid line with arrowhead
-->>
Dotted line with arrowhead
-x
Solid line with a cross at the end (async)
--x
Dotted line with a cross at the end (async)
2.4 Activations
Feature
Diagram
Activate and deactivate an actor.
sequenceDiagram
Alice->>John: Hello John, how are you?
activate John
John-->>Alice: Great!
deactivate John
Shortcut notation by appending `+/-` suffix to the message arrow.
sequenceDiagram
Alice->>+John: Hello John, how are you?
John-->>-Alice: Great!
Activations can be stacked for same actor:
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!
2.5 Notes
Add notes to a sequence diagram by the notation Note.
Note [ right of | left of | over ] [Actor]: Text in note content
Right Side
sequenceDiagram participant John Note right of John: Text in note
sequenceDiagram participant John Note right of John: Text in note
Left Side
sequenceDiagram participant John Note left of John: Text in note
sequenceDiagram participant John Note left of John: Text in note
Over
sequenceDiagram participant John Note over John: Text in note
sequenceDiagram participant John Note over John: Text in note
Create notes spanning two participants
sequenceDiagram Alice->>John: Hello John, how are you? Note over Alice,John: A typical interaction
sequenceDiagram Alice->>John: Hello John, how are you? Note over Alice,John: A typical interaction
2.6 Loops
Express loops in a sequence diagram by the notation loop.
loop Loop text... statements ...end
sequenceDiagram Alice->John: Hello John, how are you? loop Every minute John-->Alice: Great! end
sequenceDiagram Alice->John: Hello John, how are you? loop Every minute John-->Alice: Great! end
2.7 Alt
Express alternative paths in a sequence diagram by the notation alt.
alt Describing text... statements ...else... statements ...end
Or, if there is sequence that is optional (if without else).
opt Describing text... statements ...end
Example:
sequenceDiagram Alice->>John: Hello John, how are you? alt is sick John->>Alice: Not so good :( else is well John->>Alice: Feeling fresh like a daisy end opt Extra response John->>Alice: Thanks for asking end
sequenceDiagram Alice->>John: Hello John, how are you? alt is sick John->>Alice: Not so good :( else is well John->>Alice: Feeling fresh like a daisy end opt Extra response John->>Alice: Thanks for asking end
4. Demos
graph TB sq[Square shape] --> ci((Circle shape)) subgraph A od>Odd shape]-- Two line<br/>edge comment --> ro di{Diamond with <br/> line break} -.-> ro(Rounded<br>square<br>shape) di==>ro2(Rounded square shape) end %% Notice that no text in shape are added here instead that is appended further down e --> od3>Really long text with linebreak<br>in an Odd shape] %% Comments after double percent signs e((Inner / circle<br>and some odd <br>special characters)) --> f(,.?!+-\*ز) cyr[Cyrillic]-->cyr2((Circle shape Начало)); classDef green fill:#9f6,stroke:#333,stroke-width:2px classDef orange fill:#f96,stroke:#333,stroke-width:4px class sq,e green class di orange
4.4 Basic Sequence Diagram
sequenceDiagram
Alice ->> Bob: Hello Bob, how are you?
Bob-->>John: How about you John?
Bob--x Alice: I am good thanks!
Bob-x John: I am good thanks!
Note right of John: Bob thinks a long<br/>long time, so long<br/>that the text does<br/>not fit on a row.
Bob-->Alice: Checking with John...
Alice->John: Yes... John, how are you?
sequenceDiagram Alice ->> Bob: Hello Bob, how are you? Bob-->>John: How about you John? Bob--x Alice: I am good thanks! Bob-x John: I am good thanks! Note right of John: Bob thinks a long<br/>long time, so long<br/>that the text does<br/>not fit on a row. Bob-->Alice: Checking with John... Alice->John: Yes... John, how are you?
4.5 Message to Self in Loop
sequenceDiagram
participant Alice
participant Bob
Alice->>John: Hello John, how are you?
loop Healthcheck
John->>John: Fight against hypochondria
end
Note right of John: Rational thoughts<br/>prevail...
John-->>Alice: Great!
John->>Bob: How about you?
Bob-->>John: Jolly good!
sequenceDiagram participant Alice participant Bob Alice->>John: Hello John, how are you? loop Healthcheck John->>John: Fight against hypochondria end Note right of John: Rational thoughts<br/>prevail... John-->>Alice: Great! John->>Bob: How about you? Bob-->>John: Jolly good!