class

A UML class diagram (UML 2.5.1, chapters 9 to 12): classes, interfaces and enumerations with their members, packages, and the relations between them. Diagrist lays it out by itself in layers: superclasses, interfaces, wholes and users above, associated classes side by side, each package as one block.

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

The first line

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

Every class 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 the same layout as cards with a toned name field and toned packages.
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 class "Title"

Statements

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

Statement	Where	What it does
class	top level	A class: a box with the name, below it the compartments of attributes and operations, shown even when empty.
interface	top level	An interface: «interface» above the name, operations in italics; the attribute compartment only when it holds something.
enum	top level	An enumeration: «enumeration» above the name, below it one value per line.
package	top level	A package: a frame with a tab holding the name, around the classifiers in it.
assoc	top level	An n-ary association: a diamond joined to three or more classes.
rel	top level	A relation between classifiers, read from from to to; the arrow says which (see the arrows).
note	top level	A comment on a classifier: a dashed box above it with a tip down to it, below it when lines run above.
adr	top level	An architecture decision in the bar below the picture: question, the chosen option after =, and the consequence after =>.

class

class <id> <label> [in <ref>] [stereotype=<text>] [template=<text>] [tone=<choice>] [mark=<ref>] [abstract] [emph]

A class: a box with the name, below it the compartments of attributes and operations, shown even when empty. Members follow indented, one per line. Diagrist places classifiers in layers: superclasses and interfaces above, the whole above its parts, the user above what it uses, associated classes side by side. UML 2.5.1: 11.4.4 Class with compartments for attributes and operations.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that rel, note and class= use for this classifier.
<label>	argument	a text in double quotes like "Order service"	Name shown in the box.
in <ref>	clause	the id of a package declared in this diagram	The package the classifier belongs to.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: entity shows «entity».
template=	attribute	a text in double quotes like "Order service"	Template parameters such as "T" or "K, V", drawn in a dashed box at the top right corner. UML 2.5.1: 7.3.4 Template parameters in a dashed box at the top right corner.
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the name field in look=cards; without it slate.
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 beside it.
abstract	flag		An abstract classifier: the name in italics with {abstract} below it. UML 2.5.1: 9.2.4 Abstract classifier, its name in italics.
emph	flag		Highlights the box in the accent colour.

Example:

class order "Order" stereotype="entity"
  "- number : String {readOnly}"
  "+ total() : Money"

Indented lines that start without one of these keywords have this form:

<text> [static] [abstract]

A member of the classifier as a UML text in double quotes, one per line: an attribute "- name : Type" or an operation "+ total(tax : Rate) : Money". Visibility (+ - # ~) and the operation (by its parenthesis) are read from the text, as are multiplicities and properties such as [1..*] and {readOnly}. In an enum each line is a value. Members never wrap; the box grows to the widest one. UML 2.5.1: 9.5.4 Attribute with visibility, type, multiplicity and properties, 9.6.4 Operation with visibility, parameters, return type and properties.

Part	Kind	Value	Meaning
<text>	argument	a text in double quotes like "Order service"	The member as UML writes it, such as "- iban : String {readOnly}".
static	flag		A member of the class, not of its instances: drawn underlined. UML 2.5.1: 9.4.4 Static feature, underlined.
abstract	flag		An operation without implementation: drawn in italics. Only in abstract classes and interfaces. UML 2.5.1: 9.6.4 Abstract operation, in italics.

Examples:

"- name : String"
"+ total() : Money" abstract

interface

interface <id> <label> [in <ref>] [stereotype=<text>] [template=<text>] [tone=<choice>] [mark=<ref>] [abstract] [emph]

An interface: «interface» above the name, operations in italics; the attribute compartment only when it holds something. Members follow indented, one per line. Diagrist places classifiers in layers: superclasses and interfaces above, the whole above its parts, the user above what it uses, associated classes side by side. UML 2.5.1: 10.4.4 Interface with the keyword «interface».

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that rel, note and class= use for this classifier.
<label>	argument	a text in double quotes like "Order service"	Name shown in the box.
in <ref>	clause	the id of a package declared in this diagram	The package the classifier belongs to.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: entity shows «entity».
template=	attribute	a text in double quotes like "Order service"	Template parameters such as "T" or "K, V", drawn in a dashed box at the top right corner. UML 2.5.1: 7.3.4 Template parameters in a dashed box at the top right corner.
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the name field in look=cards; without it slate.
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 beside it.
abstract	flag		An abstract classifier: the name in italics with {abstract} below it. UML 2.5.1: 9.2.4 Abstract classifier, its name in italics.
emph	flag		Highlights the box in the accent colour.

Example:

interface printable "Printable"
  "+ print() : String"

Indented lines that start without one of these keywords have this form:

<text> [static] [abstract]

A member of the classifier as a UML text in double quotes, one per line: an attribute "- name : Type" or an operation "+ total(tax : Rate) : Money". Visibility (+ - # ~) and the operation (by its parenthesis) are read from the text, as are multiplicities and properties such as [1..*] and {readOnly}. In an enum each line is a value. Members never wrap; the box grows to the widest one. UML 2.5.1: 9.5.4 Attribute with visibility, type, multiplicity and properties, 9.6.4 Operation with visibility, parameters, return type and properties.

Part	Kind	Value	Meaning
<text>	argument	a text in double quotes like "Order service"	The member as UML writes it, such as "- iban : String {readOnly}".
static	flag		A member of the class, not of its instances: drawn underlined. UML 2.5.1: 9.4.4 Static feature, underlined.
abstract	flag		An operation without implementation: drawn in italics. Only in abstract classes and interfaces. UML 2.5.1: 9.6.4 Abstract operation, in italics.

Examples:

"- name : String"
"+ total() : Money" abstract

enum

enum <id> <label> [in <ref>] [stereotype=<text>] [template=<text>] [tone=<choice>] [mark=<ref>] [abstract] [emph]

An enumeration: «enumeration» above the name, below it one value per line. Members follow indented, one per line. Diagrist places classifiers in layers: superclasses and interfaces above, the whole above its parts, the user above what it uses, associated classes side by side. UML 2.5.1: 10.2.4 Enumeration with its literals.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that rel, note and class= use for this classifier.
<label>	argument	a text in double quotes like "Order service"	Name shown in the box.
in <ref>	clause	the id of a package declared in this diagram	The package the classifier belongs to.
stereotype=	attribute	a text in double quotes like "Order service"	Stereotype above the name, written without guillemets: entity shows «entity».
template=	attribute	a text in double quotes like "Order service"	Template parameters such as "T" or "K, V", drawn in a dashed box at the top right corner. UML 2.5.1: 7.3.4 Template parameters in a dashed box at the top right corner.
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of the name field in look=cards; without it slate.
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 beside it.
abstract	flag		An abstract classifier: the name in italics with {abstract} below it. UML 2.5.1: 9.2.4 Abstract classifier, its name in italics.
emph	flag		Highlights the box in the accent colour.

Example:

enum status "Status"
  "OPEN"
  "PAID"

Indented lines that start without one of these keywords have this form:

<text> [static] [abstract]

A member of the classifier as a UML text in double quotes, one per line: an attribute "- name : Type" or an operation "+ total(tax : Rate) : Money". Visibility (+ - # ~) and the operation (by its parenthesis) are read from the text, as are multiplicities and properties such as [1..*] and {readOnly}. In an enum each line is a value. Members never wrap; the box grows to the widest one. UML 2.5.1: 9.5.4 Attribute with visibility, type, multiplicity and properties, 9.6.4 Operation with visibility, parameters, return type and properties.

Part	Kind	Value	Meaning
<text>	argument	a text in double quotes like "Order service"	The member as UML writes it, such as "- iban : String {readOnly}".
static	flag		A member of the class, not of its instances: drawn underlined. UML 2.5.1: 9.4.4 Static feature, underlined.
abstract	flag		An operation without implementation: drawn in italics. Only in abstract classes and interfaces. UML 2.5.1: 9.6.4 Abstract operation, in italics.

Examples:

"- name : String"
"+ total() : Money" abstract

package

package <id> <label> [in <ref>] [tone=<choice>]

A package: a frame with a tab holding the name, around the classifiers in it. Packages nest with in. Between packages, and between a package and a classifier, only dependencies --> exist, optionally with import or access. A package without classifiers is not drawn. UML 2.5.1: 12.2.4 Package as a frame with its name in the tab.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that in, rel and note use for this package.
<label>	argument	a text in double quotes like "Order service"	Name shown in the tab.
in <ref>	clause	the id of a package declared in this diagram	The package this one is nested in.
tone=	attribute	one of blue, indigo, purple, maroon, green, teal, slate, red, orange, peach, sky	Colour of its area in look=cards; without it slate.

Examples:

package domain "domain"
package persistence "persistence" in backend

assoc

assoc <id> [label] [in <ref>] [class=<ref>] [mark=<ref>] [emph]

An n-ary association: a diamond joined to three or more classes. Each end is a leg rel <assoc> -- <class> card=... role=...; multiplicity and role stand at the class end and say how many objects there belong to one fixed combination of the other ends. The name stands at the top right of the diamond. Diagrist places the diamond in the middle of its ends: the first two left and right, the third below, the fourth (or the association class) above. UML 2.5.1: 11.5.4 N-ary association as a diamond with a leg to each end.

Written at the top level.

Part	Kind	Value	Meaning
<id>	argument	an identifier like api (letters, digits, _ and -, starting with a letter)	Id that the legs rel <id> -- <class> use.
[label]	optional argument	a text in double quotes like "Order service"	Name of the association, shown at the top right of the diamond.
in <ref>	clause	the id of a package declared in this diagram	The package the association belongs to.
class=	attribute	the id of a class declared in this diagram	The association class: a class that is this association, joined dashed to the diamond. UML 2.5.1: 11.5.4 Association class joined by a dashed line.
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 beside it.
emph	flag		Highlights the diamond in the accent colour.

Example:

assoc lesson "Lesson" class=unit

rel

rel <from> <arrow> <to> [label] [source=<multiplicity>] [card=<multiplicity>] [role=<text>] [srole=<text>] [nonav=<from|to|both>] [class=<ref>] [import] [access] [emph]

A relation between classifiers, read from from to to; the arrow says which (see the arrows). card= and role= stand at to, source= and srole= at from. Generalizations and realizations with the same target share one triangle. A relation of a class with itself is a loop. A leg of an n-ary association runs from the assoc to a class.

Written at the top level.

Part	Kind	Value	Meaning
<from>	argument	the id of a class, interface, enum, assoc or package declared in this diagram	Classifier, n-ary association or package the relation starts at.
<arrow>	argument	one of the arrows -- association, navigability open at both ends, -> directed association, navigable towards to (open head there), <-> association navigable at both ends (open heads at both), --> dependency, dashed with an open head at to; between packages with import or access, -|> generalization: from is a special kind of to, hollow triangle at to, --|> realization: from implements the interface to, dashed with a hollow triangle, o-- aggregation: from is the whole, hollow diamond at from, *-- composition: from is the whole that owns its parts, filled diamond at from	What kind of relation it is. UML 2.5.1: -- 11.5.4 Binary association as a line with its name; -> 11.5.4 Binary association as a line with its name, 11.5.4 Navigable end with an open arrowhead; <-> 11.5.4 Binary association as a line with its name, 11.5.4 Navigable end with an open arrowhead; --> 7.7.4 Dependency as a dashed arrow; -|> 9.2.3.2 Generalization between classifiers; --|> 10.4.4 Realization of an interface, dashed with a hollow triangle; o-- 11.5.4 Shared aggregation with a hollow diamond at the whole; *-- 11.5.4 Composition with a filled diamond at the whole.
<to>	argument	the id of a class, interface, enum, assoc or package declared in this diagram	Classifier, n-ary association or package the relation points to.
[label]	optional argument	a text in double quotes like "Order service"	Name of the relation, shown at the middle of the line.
source=	attribute	a UML multiplicity like 1, 0..1, 1..* or *, the lower bound not above the upper one	Multiplicity at from: how many from belong to one to. UML 2.5.1: 7.5.4 Multiplicity at an end or of a property.
card=	attribute	a UML multiplicity like 1, 0..1, 1..* or *, the lower bound not above the upper one	Multiplicity at to: how many to belong to one from. UML 2.5.1: 7.5.4 Multiplicity at an end or of a property.
role=	attribute	a text in double quotes like "Order service"	Role name at to, written opposite the multiplicity. UML 2.5.1: 11.5.4 Role name at an end of an association.
srole=	attribute	a text in double quotes like "Order service"	Role name at from. UML 2.5.1: 11.5.4 Role name at an end of an association.
nonav=	attribute	one of from, to, both	Ends that are not navigable: a small x shortly before the end. Only on associations, never at an end with an arrowhead. UML 2.5.1: 11.5.4 Non-navigable end with a small x.
class=	attribute	the id of a class declared in this diagram	The association class: a class that is this association too, joined dashed to the middle of the line and placed below it. UML 2.5.1: 11.5.4 Association class joined by a dashed line.
import	flag		A package import «import» on a dependency -->. UML 2.5.1: 7.4.4 Package import with the keyword «import» or «access».
access	flag		A private package import «access» on a dependency -->. UML 2.5.1: 7.4.4 Package import with the keyword «import» or «access».
emph	flag		Highlights the line in the accent colour.

The values of arrow and what they mean:

Value	Meaning
--	association, navigability open at both ends
->	directed association, navigable towards to (open head there)
<->	association navigable at both ends (open heads at both)
-->	dependency, dashed with an open head at to; between packages with import or access
-|>	generalization: from is a special kind of to, hollow triangle at to
--|>	realization: from implements the interface to, dashed with a hollow triangle
o--	aggregation: from is the whole, hollow diamond at from
*--	composition: from is the whole that owns its parts, filled diamond at from

Examples:

rel customer -- order "places" source=1 card=0..*
rel order *-- item source=1 card=1..*
rel invoice -|> document
rel repo --|> port
rel student -- course "takes" source=* card=* class=enrolment
rel web --> domain import

note

note <text> [on <ref>]

A comment on a classifier: a dashed box above it with a tip down to it, below it when lines run above. UML 2.5.1: 7.2.3.2 Comment (note).

Written at the top level.

Part	Kind	Value	Meaning
<text>	argument	a text in double quotes like "Order service"	What the note says, in one line.
on <ref>	clause	the id of a class, interface or enum declared in this diagram	The classifier the note belongs to. Required.

Example:

note "Exactly one lecturer per lesson" on lecturer

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 class report these. An error stops the build; a warning is printed and the picture is still drawn.

Code	Severity	What it checks
U410	error	A realization --|> runs from a class or enumeration to an interface: its target is an interface, its source is none. UML 2.5.1: 10.4.4 Realization of an interface, dashed with a hollow triangle.
U411	error	A generalization -|> joins classifiers of one kind (class with class, interface with interface) and runs in no cycle; the triangle points at the more general one. A class implements an interface with --|>. UML 2.5.1: 9.2.3.2 Generalization between classifiers.
U412	error	Only operations are abstract, and only in abstract classes and interfaces: an abstract operation of a concrete class has no implementation anywhere. UML 2.5.1: 9.6.4 Abstract operation, in italics.
U413	error	A member is a UML text: [visibility] name : Type for an attribute, [visibility] name(p : Type) : Type for an operation; a value of an enumeration is a plain name without static or abstract. UML 2.5.1: 9.5.4 Attribute with visibility, type, multiplicity and properties, 9.6.4 Operation with visibility, parameters, return type and properties, 10.2.4 Enumeration with its literals.
U414	error	Generalization, realization and dependency join types, not objects: their ends have no multiplicity and no role. UML 2.5.1: 7.7.4 Dependency as a dashed arrow, 9.2.3.2 Generalization between classifiers, 10.4.4 Realization of an interface, dashed with a hollow triangle.
U415	error	A part belongs to at most one whole at a time: the multiplicity at the whole of a composition *-- is 1 or 0..1. UML 2.5.1: 11.5.4 Composition with a filled diamond at the whole.
U416	error	A classifier names each attribute once and each operation once per list of parameter types; overloads with other parameter types are allowed. UML 2.5.1: 9.5.4 Attribute with visibility, type, multiplicity and properties, 9.6.4 Operation with visibility, parameters, return type and properties.
U417	error	An association class is an association and a class at once: class= stands on an association between classifiers or on an assoc, names a class (the table allows no other) that is none of its own ends, and each association class belongs to exactly one association. UML 2.5.1: 11.5.4 Association class joined by a dashed line.
U418	error	A package is no classifier: it is an end of dependencies --> only. import and access mark package imports, so they belong to dependencies -->. UML 2.5.1: 12.2.4 Package as a frame with its name in the tab, 7.4.4 Package import with the keyword «import» or «access».
U419	error	A package already holds its members; a dependency between a package and its own content says nothing. UML 2.5.1: 12.2.4 Package as a frame with its name in the tab, 7.7.4 Dependency as a dashed arrow.
U470	error	An end is navigable (open head), not navigable (x) or open. An x at an end with an arrowhead contradicts itself, and generalization, realization and dependency have no navigable ends. UML 2.5.1: 11.5.4 Navigable end with an open arrowhead, 11.5.4 Non-navigable end with a small x.
U471	error	A note in a class diagram is a comment on one classifier: it names it with on. UML 2.5.1: 7.2.3.2 Comment (note).
U910	warning	UML allows ends without multiplicity; exam practice, like the learning platform, asks for both ends of an association, aggregation or composition. A leg of an n-ary association needs it at the class end only. UML 2.5.1: 7.5.4 Multiplicity at an end or of a property.
U911	warning	Two relations between the same classifiers can only be told apart by a name or a role. UML 2.5.1: 11.5.4 Binary association as a line with its name, 11.5.4 Role name at an end of an association.
U912	warning	Packages should depend on each other without cycles (acyclic dependencies principle). Dependencies --> between packages and between classifiers of different packages count; UML allows cycles, so it is a warning, once per cycle. UML 2.5.1: 12.2.4 Package as a frame with its name in the tab.
U913	warning	A package without classifiers, also in its nested packages, has no frame: it is not drawn, and relations to it are left out. UML 2.5.1: 12.2.4 Package as a frame with its name in the tab.
U916	warning	{readOnly} makes an attribute unchangeable, {query} an operation free of side effects. Swapped, neither says anything; the text is drawn as written. UML 2.5.1: 9.5.4 Attribute with visibility, type, multiplicity and properties, 9.6.4 Operation with visibility, parameters, return type and properties.
U917	warning	An n-ary association joins three or more ends. With two legs it is a binary association, drawn as a line without diamond. UML 2.5.1: 11.5.4 N-ary association as a diamond with a leg to each end.
U918	warning	A leg of an n-ary association is a line from the diamond to a class: --, or -> towards the class. Name and association class belong to the diamond, multiplicity and role to the class end; aggregation and composition exist only between two ends. UML 2.5.1: 11.5.4 N-ary association as a diamond with a leg to each end.