Message
A message is a horizontal arrow between lifelines, its kind shown by the line and head.
| Arrow | Message | Line and head |
|---|---|---|
a -> b | synchronous call | solid, filled head |
a ->> b | asynchronous | solid, open head |
a --> b | reply | dashed, open head |
[-> a | found (from outside the diagram) | filled circle at the start |
a ->] | lost (leaves the diagram) | filled circle at the end |
diagram sequence "Message kinds"
participant Client
participant Server
[-> Client : wake
Client -> Server : call()
Server --> Client : reply
Client ->> Server : notify
Server ->] : lost
A self-message draws a compact loop on its lifeline.
Syntax
<a> (-> | ->> | -->) <b> [: label] [{ ... }]
[-> <a> [: label] [{ ... }]
<a> ->] [: label]
A label runs to the end of the line, apart from a comment or a space-separated { or }; quote it to
keep those as text.
Specification
UML 2.5.1, 17.4.4.1 (p. 576): filled heads for synchronous, open for asynchronous and dashed lines for reply. Found and lost messages end on a small black circle (17.4.4, p. 577).