Note

A note is a rectangle with its upper right corner folded, joined to its target by a dashed line. It attaches free text to an element, and drumlin wraps the text.

component Cache
note Cache: Write-through. Entries expire after 30 seconds.

A note sits next to its target, inside the same container.

package "Storage" {
  component Journal
  component Pages
  Journal --> Pages
  note Journal: fsync before every commit record.
}

Attach several notes where they help.

component Reader
component Writer
Reader --> Writer : wakes
note Reader: Lock-free. May retry.
note Writer: Single owner only.

Other kinds

Notes work in every diagram kind, with the syntax of that kind:

diagram state "A note on a state"
[*] --> Idle
Idle --> [*]
note Idle: Waits here between jobs.

In a sequence diagram, write note over a: text, note left of a: text or note right of a: text. There the line is suppressed, as the spec allows when the context is clear. In an activity diagram, write note: text after a statement to attach it.

Syntax

note <target>: text        component, package and state diagrams
note over <a>[, <b>]... : text        sequence diagrams
note left of <a>: text
note right of <a>: text
note: text                 activity diagrams, on the statement before it

Specification

UML 2.5.1, 7.2.4 (p. 22): a Comment is a rectangle with the upper right corner bent, connected by a dashed line, which may be suppressed if the context is clear.

Used in

Storage engine, Layered architecture, Process lifecycle, TCP connection, Build and release pipeline.