sequence

A UML sequence diagram (UML 2.5.1, chapter 17): lifelines from left to right in source order, messages and fragments from top to bottom. Fragments nest by indentation.

This page lists everything a sequence diagram may contain. The same grammar is available as data with dgr grammar sequence --json, and the overview explains how lines, texts and attributes are written and lists the codes every kind shares.

The first line

diagram sequence "Title" [subtitle=<text>] [look=<plain|cards>] [locale=<en|de>]

Every sequence diagram starts with this line.

Part	Kind	Value	Meaning
subtitle=	attribute	a text in double quotes like "Order service"	Second line below the title.
look=	attribute	one of plain, cards	plain (default) draws the UML notation, cards toned cards.
locale=	attribute	one of en, de	Language of the texts Diagrist adds to the picture and of the description: en (default) or de.

Example:

diagram sequence "Title"

Statements

Each statement is one line that starts with its keyword. Statements inside blocks are indented below them. Like every kind, sequence also has use, variant, set and drop, described in the overview.

Statement	Where	What it does
participant	top level	A lifeline drawn as a box, from left to right in source order.
actor	top level	A lifeline drawn as a stick figure, from left to right in source order.
database	top level	A lifeline drawn as a cylinder, from left to right in source order.
queue	top level	A lifeline drawn as a horizontal tube, from left to right in source order.
boundary	top level	A lifeline drawn as the boundary symbol of robustness analysis, from left to right in source order.
control	top level	A lifeline drawn as the control symbol of robustness analysis, from left to right in source order.
entity	top level	A lifeline drawn as the entity symbol of robustness analysis, from left to right in source order.
autonumber	top level	Numbers all messages in source order (1, 2, 3 …), across fragments; the number stands before the label.
frame	top level	A frame around the whole interaction with sd Name in its tag.
msg	top level and inside blocks	A message in source order; its arrow says what kind.
create	top level and inside blocks	A creation message: dashed with an open head, and the head of the receiver stands at its height.
destroy	top level and inside blocks	Destruction: the lifeline ends here with an X.
activate	top level and inside blocks	Starts an activation bar by hand, for processing after an asynchronous message.
deactivate	top level and inside blocks	Ends the bar the last activate of this lifeline started.
note	top level and inside blocks	A note at this point of the time axis, over the lifelines of over=.
ref	top level and inside blocks	A reference to another interaction (interaction use): a frame tagged ref over the lifelines of over=.
invariant	top level and inside blocks	A state invariant at this point on the lifeline on=: a condition in {...}, or with state a state in a rounded box.
divider	top level	A divider on the time axis: a double line across all lifelines with the text in a box in the middle.
coregion	top level and inside blocks	A coregion on the lifeline: the order of the indented events is arbitrary, drawn as square brackets on the lifeline.
alt	top level and inside blocks	Alternatives: the first operand whose guard holds is taken; further operands start with else.
else	inside alt	The next operand of alt, written inside alt with its statements indented below it.
opt	top level and inside blocks	An optional part, taken when its guard holds.
loop	top level and inside blocks	A repetition while the guard holds.
par	top level and inside blocks	Parallel operands, separated by and; their events interleave freely.
and	inside par, seq, strict	The next operand of par, seq or strict, written inside the fragment with its statements indented below it.
break	top level and inside blocks	Ends the enclosing interaction when the guard holds.
critical	top level and inside blocks	A critical region: its events are not interleaved.
seq	top level and inside blocks	Weak sequencing of operands, separated by and.
strict	top level and inside blocks	Strict sequencing of operands, separated by and.
neg	top level and inside blocks	An invalid trace: what must not happen.
assert	top level and inside blocks	The only valid trace at this point.
ignore	top level and inside blocks	Messages that may appear anywhere and are ignored; the guard lists their names and shows as ignore {...}.
consider	top level and inside blocks	Only the listed messages are considered; the guard lists their names and shows as consider {...}.
duration	top level	A duration constraint between two messages with id=: a bracket from the first to the second, left of the lifeline both touch when there is room, otherwise mirrored to the right or at the left edge.
time	top level	A time constraint of one message with id=: a tick at its height left of its lifeline or at the left edge, the text in {...}.
adr	top level	An architecture decision in the bar below the picture: question, the chosen option after =, and the consequence after =>.

participant

participant <id> <label> [stereotype=<text>] [tone=<choice>] [external]

A lifeline drawn as a box, from left to right in source order. Messages, notes and references name it by its id. UML 2.5.1: 17.3.3.1 Lifeline.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that messages, activate, note and ref use for this lifeline.
<label>	argument	a text in double quotes like "Order service"	Name shown in the head.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: service shows «service».
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the head and its bars in look=cards; without it the head is slate.
external	flag		Draws the head dashed: the system is outside the scope of the diagram.

Example:

participant api "api-service" stereotype="service"

actor

actor <id> <label> [stereotype=<text>] [tone=<choice>] [external]

A lifeline drawn as a stick figure, from left to right in source order. Messages, notes and references name it by its id. UML 2.5.1: 17.3.3.1 Lifeline.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that messages, activate, note and ref use for this lifeline.
<label>	argument	a text in double quotes like "Order service"	Name shown in the head.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: service shows «service».
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the head and its bars in look=cards; without it the head is slate.
external	flag		Draws the head dashed: the system is outside the scope of the diagram.

Example:

actor customer "Customer"

database

database <id> <label> [stereotype=<text>] [tone=<choice>] [external]

A lifeline drawn as a cylinder, from left to right in source order. Messages, notes and references name it by its id. UML 2.5.1: 17.3.3.1 Lifeline.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that messages, activate, note and ref use for this lifeline.
<label>	argument	a text in double quotes like "Order service"	Name shown in the head.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: service shows «service».
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the head and its bars in look=cards; without it the head is slate.
external	flag		Draws the head dashed: the system is outside the scope of the diagram.

Example:

database db "Orders DB"

queue

queue <id> <label> [stereotype=<text>] [tone=<choice>] [external]

A lifeline drawn as a horizontal tube, from left to right in source order. Messages, notes and references name it by its id. UML 2.5.1: 17.3.3.1 Lifeline.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that messages, activate, note and ref use for this lifeline.
<label>	argument	a text in double quotes like "Order service"	Name shown in the head.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: service shows «service».
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the head and its bars in look=cards; without it the head is slate.
external	flag		Draws the head dashed: the system is outside the scope of the diagram.

Example:

queue broker "Kafka"

boundary

boundary <id> <label> [stereotype=<text>] [tone=<choice>] [external]

A lifeline drawn as the boundary symbol of robustness analysis, from left to right in source order. Messages, notes and references name it by its id. UML 2.5.1: 17.3.3.1 Lifeline.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that messages, activate, note and ref use for this lifeline.
<label>	argument	a text in double quotes like "Order service"	Name shown in the head.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: service shows «service».
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the head and its bars in look=cards; without it the head is slate.
external	flag		Draws the head dashed: the system is outside the scope of the diagram.

Example:

boundary form "Order form"

control

control <id> <label> [stereotype=<text>] [tone=<choice>] [external]

A lifeline drawn as the control symbol of robustness analysis, from left to right in source order. Messages, notes and references name it by its id. UML 2.5.1: 17.3.3.1 Lifeline.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that messages, activate, note and ref use for this lifeline.
<label>	argument	a text in double quotes like "Order service"	Name shown in the head.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: service shows «service».
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the head and its bars in look=cards; without it the head is slate.
external	flag		Draws the head dashed: the system is outside the scope of the diagram.

Example:

control checkout "Checkout"

entity

entity <id> <label> [stereotype=<text>] [tone=<choice>] [external]

A lifeline drawn as the entity symbol of robustness analysis, from left to right in source order. Messages, notes and references name it by its id. UML 2.5.1: 17.3.3.1 Lifeline.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that messages, activate, note and ref use for this lifeline.
<label>	argument	a text in double quotes like "Order service"	Name shown in the head.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: service shows «service».
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the head and its bars in look=cards; without it the head is slate.
external	flag		Draws the head dashed: the system is outside the scope of the diagram.

Example:

entity order "Order"

autonumber

autonumber

Numbers all messages in source order (1, 2, 3 …), across fragments; the number stands before the label.

Written at the top level.

Example:

autonumber

frame

frame [label]

A frame around the whole interaction with sd Name in its tag. Without a name it shows the title. Gates (gate in msg) draw the frame without this line too. UML 2.5.1: 17.2.3.1 Interaction, drawn as a frame.

Written at the top level.

Part	Kind	Value	Meaning
[label]	optional argument	a text in double quotes like "Order service"	Name of the interaction in the tag; defaults to the title.

Example:

frame "OAuth callback"

msg

msg <from> <arrow> <to> [label] [id=<id>] [mark=<ref>] [duration=<text>] [emph]

A message in source order; its arrow says what kind. Sender equal to receiver is a self call. Calls and replies activate the receiver by themselves. found as sender and lost as receiver are found and lost messages; gate is a gate on the frame of the interaction (gate -> a comes in from the left, a --> gate replies to the left, a -> gate leaves to the right), gate.name names it. The id= of a ref or fragment as an end leads the message to its edge. UML 2.5.1: 17.4.3.1 Message.

Written at the top level and inside coregion, alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<from>	argument	a lifeline id like api, found, lost, gate, gate.name, or the id= of a ref or fragment, optionally with .name	Sender: a lifeline, found, gate, or a frame with id=. UML 2.5.1: found 17.4.3.1 Found message, without sender; gate 17.4.3.5 Gate on the frame of the interaction.
<arrow>	argument	one of the arrows -> synchronous call (filled head), ~> asynchronous message (open head), --> reply (dashed, open head)	The kind of message, which also decides how it is drawn. UML 2.5.1: -> 17.4.3.1 Synchronous call; ~> 17.4.3.1 Asynchronous call or signal; --> 17.4.3.1 Reply to a call.
<to>	argument	a lifeline id like api, found, lost, gate, gate.name, or the id= of a ref or fragment, optionally with .name	Receiver: a lifeline, lost, gate, or a frame with id=. UML 2.5.1: lost 17.4.3.1 Lost message, without receiver; gate 17.4.3.5 Gate on the frame of the interaction.
[label]	optional argument	a text in double quotes like "Order service"	What is sent; without it the arrow has no label.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the message that duration and time refer to.
mark=	attribute	the id of an adr declared in this diagram	Id of a decision of the decision bar, such as E1; the mark is drawn after the label.
duration=	attribute	a text in double quotes like "Order service"	Duration of the transmission: the arrow slopes down and shows the text in {...}. UML 2.5.1: 8.5.3.2 Duration constraint.
emph	flag		Highlights the message in the accent colour.

The values of arrow and what they mean:

Value	Meaning
->	synchronous call (filled head)
~>	asynchronous message (open head)
-->	reply (dashed, open head)

Examples:

msg client -> api "GET /orders" id=request
msg api --> client "200 OK"
msg gate.order -> api "place(order)" emph

create

create <from> <arrow> <to> [label] [id=<id>] [mark=<ref>] [duration=<text>] [emph]

A creation message: dashed with an open head, and the head of the receiver stands at its height. Before it the lifeline does not exist. UML 2.5.1: 17.4.3.1 Message that creates a lifeline.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<from>	argument	the id of a participant, actor, database, queue, boundary, control or entity declared in this diagram	The lifeline that creates.
<arrow>	argument	one of the arrows ->	Always ->.
<to>	argument	the id of a participant, actor, database, queue, boundary, control or entity declared in this diagram	The lifeline that is created.
[label]	optional argument	a text in double quotes like "Order service"	The constructor call; without it the arrow has no label.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the message that duration and time refer to.
mark=	attribute	the id of an adr declared in this diagram	Id of a decision of the decision bar, such as E1; the mark is drawn after the label.
duration=	attribute	a text in double quotes like "Order service"	Duration of the transmission: the arrow slopes down and shows the text in {...}. UML 2.5.1: 8.5.3.2 Duration constraint.
emph	flag		Highlights the message in the accent colour.

Example:

create client -> meter "new MeterData()"

destroy

destroy <target>

Destruction: the lifeline ends here with an X. No message reaches it afterwards. UML 2.5.1: 17.4.3.4 End of a lifeline (destruction).

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<target>	argument	the id of a participant, actor, database, queue, boundary, control or entity declared in this diagram	The lifeline that ends.

Example:

destroy session

activate

activate <target>

Starts an activation bar by hand, for processing after an asynchronous message. Calls and replies need none, their bars appear by themselves. Ends with deactivate. UML 2.5.1: 17.2.3.4 Execution on a lifeline (activation bar).

Written at the top level and inside coregion, alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<target>	argument	the id of a participant, actor, database, queue, boundary, control or entity declared in this diagram	The lifeline whose bar starts at the last message.

Example:

activate worker

deactivate

deactivate <target>

Ends the bar the last activate of this lifeline started. UML 2.5.1: 17.2.3.4 Execution on a lifeline (activation bar).

Written at the top level and inside coregion, alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<target>	argument	the id of a participant, actor, database, queue, boundary, control or entity declared in this diagram	The lifeline whose bar ends at the last message.

Example:

deactivate worker

note

note <text> [over=<lifelines>]

A note at this point of the time axis, over the lifelines of over=. Long texts wrap. UML 2.5.1: 7.2.3.2 Comment (note).

Written at the top level and inside coregion, alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<text>	argument	a text in double quotes like "Order service"	What the note says.
over=	attribute	lifeline ids separated by commas without spaces, like auftrag,lager	Lifelines it spans, comma separated without spaces, like over=auftrag,lager. Required.

Example:

note "Idempotency key = order number" over=api,db

ref

ref <label> [over=<lifelines>] [id=<id>] [file=<text>]

A reference to another interaction (interaction use): a frame tagged ref over the lifelines of over=. With id=r the messages right after it that name r as an end run to its edge (actual gates, r.name names them), and the frame grows to hold them. UML 2.5.1: 17.7.3.1 Use of another interaction (ref).

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<label>	argument	a text in double quotes like "Order service"	Name of the referenced interaction.
over=	attribute	lifeline ids separated by commas without spaces, like auftrag,lager	Lifelines it spans, comma separated without spaces, like over=auftrag,lager. Required.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame, for messages that start or end at its edge. UML 2.5.1: 17.4.3.5 Gate on an interaction use.
file=	attribute	a text in double quotes like "Order service"	File of the referenced sequence diagram, relative to this one; named in the description.

Example:

ref "Authorize payment" over=payment,psp id=pay file="authorize-payment.dgr"

invariant

invariant <text> [on=<ref>] [state]

A state invariant at this point on the lifeline on=: a condition in {...}, or with state a state in a rounded box. UML 2.5.1: 17.2.3.5 State invariant.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider.

Part	Kind	Value	Meaning
<text>	argument	a text in double quotes like "Order service"	The condition or state, without braces.
on=	attribute	the id of a participant, actor, database, queue, boundary, control or entity declared in this diagram	The lifeline the invariant holds on. Required.
state	flag		Draws a state in a rounded box instead of a condition in braces.

Example:

invariant "logged in" on=bff state

divider

divider [label]

A divider on the time axis: a double line across all lifelines with the text in a box in the middle. Only at the top level, not inside a fragment.

Written at the top level.

Part	Kind	Value	Meaning
[label]	optional argument	a text in double quotes like "Order service"	Name of the section that starts here.

Example:

divider "Accept the webhook"

coregion

coregion <on>

A coregion on the lifeline: the order of the indented events is arbitrary, drawn as square brackets on the lifeline. Only messages from or to it, activate, deactivate and note may stand in it. UML 2.5.1: 17.6.4.10 Coregion, unordered events on one lifeline.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, activate, deactivate, note.

Part	Kind	Value	Meaning
<on>	argument	the id of a participant, actor, database, queue, boundary, control or entity declared in this diagram	The lifeline whose events are unordered.

Example:

coregion notify

alt

alt [guard] [id=<id>]

Alternatives: the first operand whose guard holds is taken; further operands start with else. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.7 Alternatives (alt), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider, else.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

alt "token valid"

else

else [guard]

The next operand of alt, written inside alt with its statements indented below it. Without a guard it shows [else]. A dashed line separates the operands. UML 2.5.1: 17.6.3.1 Operand of a combined fragment.

Written only inside alt. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of this operand, without brackets. UML 2.5.1: 17.6.3.2 Guard of an operand.

Example:

else "invalid token"

opt

opt [guard] [id=<id>]

An optional part, taken when its guard holds. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.8 Option (opt), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

opt "3-D Secure required"

loop

loop [guard] [id=<id>]

A repetition while the guard holds. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.17 Loop (loop), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

loop "at most 3 times" id=retry

par

par [guard] [id=<id>]

Parallel operands, separated by and; their events interleave freely. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.10 Parallel (par), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider, and.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

par

and

and [guard]

The next operand of par, seq or strict, written inside the fragment with its statements indented below it. UML 2.5.1: 17.6.3.1 Operand of a combined fragment.

Written only inside par, seq or strict. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of this operand, without brackets. UML 2.5.1: 17.6.3.2 Guard of an operand.

Example:

and

break

break [guard] [id=<id>]

Ends the enclosing interaction when the guard holds. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.9 Break (break), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

break "timeout"

critical

critical [guard] [id=<id>]

A critical region: its events are not interleaved. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.14 Critical region (critical), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

critical

seq

seq [guard] [id=<id>]

Weak sequencing of operands, separated by and. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.11 Weak sequencing (seq), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider, and.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

seq

strict

strict [guard] [id=<id>]

Strict sequencing of operands, separated by and. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.12 Strict sequencing (strict), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider, and.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

strict

neg

neg [guard] [id=<id>]

An invalid trace: what must not happen. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.13 Invalid traces (neg), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

neg

assert

assert [guard] [id=<id>]

The only valid trace at this point. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.16 Assertion (assert), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...]. UML 2.5.1: 17.6.3.2 Guard of an operand.
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

assert

ignore

ignore [guard] [id=<id>]

Messages that may appear anywhere and are ignored; the guard lists their names and shows as ignore {...}. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.15 Ignored messages (ignore), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...].
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

ignore "ping, status"

consider

consider [guard] [id=<id>]

Only the listed messages are considered; the guard lists their names and shows as consider {...}. The statements indented below it belong to the fragment; fragments nest. UML 2.5.1: 17.6.3.3 Combined fragment, 17.6.3.15 Considered messages (consider), 17.6.3.1 Operand of a combined fragment.

Written at the top level and inside alt, else, opt, loop, par, and, break, critical, seq, strict, neg, assert, ignore or consider. Indented below it: msg, create, destroy, activate, deactivate, note, ref, invariant, coregion, alt, opt, loop, par, break, critical, seq, strict, neg, assert, ignore, consider.

Part	Kind	Value	Meaning
[guard]	optional argument	a text in double quotes like "Order service"	Condition of the first operand, without brackets; Diagrist adds [...].
id=	attribute	an identifier like api (letters, digits, _ and -, starting with a letter)	Name of the frame: a message with this name as an end starts or ends at its edge (a gate of the fragment, f.name names it). UML 2.5.1: 17.4.3.5 Gate on a combined fragment.

Example:

consider "order, pay"

duration

duration <from> <to> <text>

A duration constraint between two messages with id=: a bracket from the first to the second, left of the lifeline both touch when there is room, otherwise mirrored to the right or at the left edge. The text is written without braces; Diagrist adds {...}. UML 2.5.1: 8.5.3.2 Duration constraint.

Written at the top level.

Part	Kind	Value	Meaning
<from>	argument	the id of a msg or create declared in this diagram	The earlier message.
<to>	argument	the id of a msg or create declared in this diagram	The later message.
<text>	argument	a text in double quotes like "Order service"	The constraint, without braces.

Example:

duration request response "≤ 300 ms"

time

time <at> <text>

A time constraint of one message with id=: a tick at its height left of its lifeline or at the left edge, the text in {...}. UML 2.5.1: 8.5.3.2 Time constraint.

Written at the top level.

Part	Kind	Value	Meaning
<at>	argument	the id of a msg or create declared in this diagram	The message.
<text>	argument	a text in double quotes like "Order service"	The constraint, without braces.

Example:

time request "t = now"

adr

adr <id> <question> <equals> <choice> [then] [consequence] [open=<text>]

An architecture decision in the bar below the picture: question, the chosen option after =, and the consequence after =>. mark= with its id puts the mark into the picture.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id of the decision, such as E1; mark=E1 refers to it.
<question>	argument	a text in double quotes like "Order service"	The question that was decided.
<equals>	argument	one of the arrows =	Separates the question from the choice.
<choice>	argument	a text in double quotes like "Order service"	The chosen option.
[then]	optional argument	one of the arrows =>	Introduces the consequence.
[consequence]	optional argument	a text in double quotes like "Order service"	What follows from the choice.
open=	attribute	a text in double quotes like "Order service"	Who still decides an open question; the card is drawn dashed.

Example:

adr E1 "How do the services coordinate?" = "Events over Kafka" => "No central coordinator"

Diagnostic codes

Besides the codes of the language and the kernel, listed in the overview, the rules of sequence report these. An error stops the build; a warning is printed and the picture is still drawn.

Code	Severity	What it checks
U400	error	Message ends and over= lists name declared lifelines. lang checks the other references; these can also be gates, so the plugin checks them. UML 2.5.1: 17.3.3.1 Lifeline.
U401	error	Inside a fragment, the statements of an operand are indented below its else or and. A statement at the level of the marker after it would silently join the operand above. UML 2.5.1: 17.6.3.1 Operand of a combined fragment.
U403	error	A reply --> answers an open synchronous call in the opposite direction; the model pairs them innermost first. UML 2.5.1: 17.4.3.1 Reply to a call, 17.4.3.1 Synchronous call.
U404	error	Before its creation and after its destruction a lifeline does not exist; each happens at most once. UML 2.5.1: 17.4.3.1 Message that creates a lifeline, 17.4.3.4 End of a lifeline (destruction).
U405	error	deactivate ends a bar that activate started on the same lifeline. UML 2.5.1: 17.2.3.4 Execution on a lifeline (activation bar).
U408	error	A lost message has no receiver, a found one no sender: lost only on the right, found only on the left, both only on a call or asynchronous message, and neither as a lifeline id. UML 2.5.1: 17.4.3.1 Lost message, without receiver, 17.4.3.1 Found message, without sender.
U450	error	A gate links a message with the frame of the interaction: gate is no lifeline id and stands at one end of a message only, never with lost, found or a creation. UML 2.5.1: 17.4.3.5 Gate on the frame of the interaction.
U451	error	ignore and consider name the messages they ignore or consider, written as their guard. UML 2.5.1: 17.6.3.15 Ignored messages (ignore), 17.6.3.15 Considered messages (consider).
U452	error	A note and a reference need over=, a state invariant needs on=: they stand on lifelines. UML 2.5.1: 17.2.3.5 State invariant, 17.7.3.1 Use of another interaction (ref).
U453	error	A coregion is the short form of a par whose operands hold one event each on the same lifeline; every message in it is sent or received by that lifeline. The tables allow only msg, activate, deactivate and note in it. UML 2.5.1: 17.6.4.10 Coregion, unordered events on one lifeline.
U454	error	A gate links a message with the edge of a reference (actual gate) or of a combined fragment. At a reference the message comes from a lifeline outside it and follows it, with only events beside it in between; at a fragment it stands inside. The frame name is its own. UML 2.5.1: 17.4.3.5 Gate on an interaction use, 17.4.3.5 Gate on a combined fragment.
U900	warning	UML allows alt and par with one operand, but opt or no fragment says it more clearly. UML 2.5.1: 17.6.3.7 Alternatives (alt), 17.6.3.10 Parallel (par).
U901	warning	UML allows leaving out the reply; it is still named. Exempt are self calls and calls made while the caller handles a call it answers later: that reply implies the inner call returned. Lost and found messages are U907. UML 2.5.1: 17.4.3.1 Synchronous call, 17.4.3.1 Reply to a call.
U902	warning	A lifeline no message, note or reference touches says nothing; remove it or add what it does. UML 2.5.1: 17.3.3.1 Lifeline.
U903	warning	An operand without events draws an empty band; fill it or remove it. UML 2.5.1: 17.6.3.1 Operand of a combined fragment.
U904	warning	In alt every operand but the last needs a guard; the last one may stand for [else]. UML 2.5.1: 17.6.3.7 Alternatives (alt), 17.6.3.2 Guard of an operand.
U905	warning	activate without deactivate: the bar reaches to the end of the diagram. UML 2.5.1: 17.2.3.4 Execution on a lifeline (activation bar).
U906	warning	A duration runs from the earlier to the later message; swapped, Diagrist still draws it. UML 2.5.1: 8.5.3.2 Duration constraint.
U907	warning	No reply can follow a lost or found message, so as a synchronous call it would wait forever; use ~>. UML 2.5.1: 17.4.3.1 Lost message, without receiver, 17.4.3.1 Found message, without sender, 17.4.3.1 Synchronous call.
U908	warning	duration= slopes the arrow. A self call is a loop and a creation ends at the head at its height: there the arrow stays level and the duration is missing from the picture. UML 2.5.1: 8.5.3.2 Duration constraint.
U909	warning	A coregion with fewer than two messages leaves no order open and says nothing. UML 2.5.1: 17.6.4.10 Coregion, unordered events on one lifeline.
U950	warning	id= on a reference or fragment only serves gates; without a message at its edge it has no effect. UML 2.5.1: 17.4.3.5 Gate on an interaction use, 17.4.3.5 Gate on a combined fragment.
U951	warning	A gate is a point on the frame with one message per side; two messages through the same named gate in the same direction leave open which one is meant. UML 2.5.1: 17.4.3.5 Gate on the frame of the interaction, 17.4.3.5 Gate on an interaction use, 17.4.3.5 Gate on a combined fragment.