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Simple signals

Draw a signal from one participant to another like this:

# This is a comment.            
Alice->Bob: Filled arrow
Alice->>Bob: Open arrow
Bob-->Alice: Dotted line
Bob-->>Alice: Dotted Line, open arrow
Bob<->Alice: Double arrow

The participants are automatically created when they are used. Use the "-->" syntax to draw a dotted line.

To include a colon in a participant name, enclose it in quotes.

":Alice"->":Bob": Hello

The next section describes how to save typing by declaring participant names.

Changing the order of participants

If you want to participants to be shown in a different order than they are used, declare them first using the participant keyword. You can also rename them this way to save typing.

participant Bob
participant Alice
participant "I have a really\nlong name" as L

Alice->Bob: Authentication Request
Bob->Alice: Authentication Response
Bob->L: Log transaction

Signal to Self

A participant can send a signal to itself. This will result in an arrow that turns back on itself.

You may break the text into multiple lines by using "\n".

Alice->Alice: This is a signal to self.\nIt also demonstrates \nmultiline \ntext.

Grouping signals together

You can group signals together using the alt/else, opt, and loop keywords. All of them can take a text description that will be displayed in the group header. Use the end keyword to signal the end of a group. The groups may be nested to any depth.

Alice->Bob: Authentication Request
alt successful case
Bob->Alice: Authentication Accepted
else some kind of failure
Bob->Alice: Authentication Failure
    loop 1000 times
        Alice->Bob: DNS Attack
else Another type of failure
Bob->Alice: Please repeat

Notes in the diagram

You can add notes to your diagram. Notes can be placed to the left of a participant or to the right of a participant. In addition, you can centre a note over one or more participants.

If a note contains more than one line, it will be not be word-wrapped. Instead, it will be formatted exactly as written.

participant Alice
participant Bob

note left of Alice 
This is displayed 
left of Alice.
end note
note right of Alice: This is displayed right of Alice.
note over Alice: This is displayed over Alice.
note over Alice, Bob: This is displayed over Bob and Alice.

Lifeline Activation and Destruction

Use the + and - with signals to denote object activation. While activated, the participant's lifeline will be highlighted. + will activate the receiver, and - will deactivate the sender.

You can use the destroy keyword to destroy a participant. The participant's lifeline will end at the previous signal.

User->+A: DoWork
A->+B: <<createRequest>>
B->+C: DoWork
C-->B: WorkDone
destroy C
B-->-A: RequestCreated
A->User: Done

Alternate Syntax

Get more control over activations using the activate and deactivate keywords. The commands apply to the previous signal.
Alice->Bob: Do some work!
activate Bob

Bob->Bob: Work routine
activate Bob
deactivate Bob

Bob->Alice: All done!
deactivate Bob

Only arrows can cause activations

Activations and deactivations attach themselves to the previous signal. Neither a note or a state can cause a deactivation. If you want to deactivate spontaneously, use a signal-to-self.
A->+B: Activate please
B->-B: I'm deactivating now\n by myself

One arrow can activate/deactivate many participants at a time

activate A
activate B

deactivate A
deactivate B
activate C

deactivate C

Extended Text Descriptions (available in a purchased version)

 You can explain the sequences that follow
 simply by indenting your explanations 
 with a space.

Alice->Bob: Wow!                

Parallel signals (available in purchased version)

You can make different things happen at the same time using the parallel keyword.

parallel {
    Client->Proxy: Request
    Proxy->Server: Forwarded Request
    note right of Server: Web proxy in operation

States (available in purchased version)

A rounded box can be useful to show state information. The syntax is identical to the note keyword, except that state is used.

participant Client
participant Server
parallel {
    state over Server: LISTEN
    state over Client: CLOSED
Client->Server: SYN
parallel { 
    state over Client: SYN-SENT
    state over Server: SYN_RECEIVED
Server->Client: ACK

Autonumbering (available in purchased version)

Autonumbering will automatically prefix all signals with a number. To use it, include the line autonumber followed by the number to start with. To turn off autonumbering, use "autonumber off"

autonumber 2
UE->GANC: Register Request
GANC->UE: Register Reject

Reference other sequences (available in purchased version)

You can summarize or refer to sequences by drawing a box over one or more participants.

ref over Mobile, Base Station
   Refer to 3GPP 44.060
end ref

You can optionally have a signal going into the box or one coming out of it.

Alice->ref over Bob, Mary: input
   refer to other diagram
end ref -->Alice: output

Footer types (available in purchased version)

Change the way the bottom of your diagram looks using option footer=.

option footer=none
option footer=bar

WebSequenceDiagrams software is provided by Hanov Solutions Inc., of Waterloo, Ontario, Canada.