Class diagrams

TL;DR

Ask your agent

Use Plotwork to draw the classes of a notification service. A Notifier queues Messages and delivers each one through a Channel. Channel is an interface with EmailChannel and SmsChannel implementing it. A Message has a Priority enum, and a Template class is abstract. Group the channels in a package, and add a note that a message is kept until every channel has confirmed delivery.

Use Plotwork to draw the Observer pattern as a class diagram. A Subject interface notifies Observer interfaces. WeatherStation implements Subject, and Display, Logger, and Alarm implement Observer. Show that the subject has many observers.

Example

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The language

A statement is words, quoted strings, key=value options, and the arrows. A # outside quotes starts a comment. Ids are letters, digits, _, and a - inside the id. A name with other characters, or with type parameters, goes in the label: class Repo "Repository<T>".

Statements

A class and a package share one set of ids, and an id used twice is error E130. A relation that names an unknown class is E131.

Class types

stereotype="service" adds a word in guillemets, such as «service». With a type that has its own word, the two share the line: «interface, service». tone= takes any tone of the theme and changes the header band. A color value is never accepted.

Members

A member is one quoted string. Its first character may be a mark that says who sees it, drawn in the gutter of the box.

A member with a parenthesis is a method, and every other member is an attribute. Attributes are drawn first and methods below a divider, whatever order you write them in. The colon after the name, or after the parameters of a method, starts the type. A colon inside brackets belongs to the name, so "+pair: Map<a:b, int>" has the type Map<a:b, int>. A flag follows the string.

1class Account {2  "-balance: Money"3  "#limit: Money"4  "+deposit(amount: Money): void"5  "+open(owner: Person): Account" static6  "+close(): void" abstract7}

Relations

Write an inheritance or a realization from the child to the parent, and a composition or an aggregation from the whole to the part. The class at the upper end is the one the layout puts first, so with direction=down parents and wholes are above.

A cardinality is a quoted string of at most 12 characters, such as "1", "0..1", "*", or "1..*". It sits beside the line at its end. The label is a pill on the line. The arrows ..> and <--> belong to flow diagrams, so a class diagram refuses them with E344 and the hint says what to write.

1Customer "1" -> "0..*" Order : "places"2Order "1" owns "1..*" Line : "contains"3Employee "0..1" -> "*" Employee : "manages"

A relation from a class to itself is a loop on the side of the box that the layers do not run through. Several classes that extend or implement the same parent, and name no cardinality at the parent, leave it in one trunk.

Every relation, each with its mark:

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Notes

A note is a card. note on Order : "A placed order cannot be edited." joins it to a class with a dotted line, and note : "Domain model, version 2." stands alone.

Limits and warnings

Warnings never stop rendering. An error stops it and the diagram is not drawn.

From Mermaid

classDiagram and classDiagram-v2 convert to a class diagram. Convert one with convert_mermaid, or a whole Markdown file with sync_markdown and convertMermaid set to true. A Mermaid front matter title: becomes the title, and accTitle and accDescr become the title and the description.

1---2title: Pets3---4classDiagram5  class Animal {6    <<abstract>>7    +String name8    +makeSound() void9  }10  class Dog11  Animal <|-- Dog12  Owner "1" --> "*" Animal : owns13  note for Dog "Good boy."

That becomes Dog extends Animal, Owner "1" -> "*" Animal : "owns", and note on Dog : "Good boy.". Animal becomes type=abstract, and the two members are turned round to +name: String and +makeSound(): void, each reported with M240.

The migration guide lists every conversion code.

See also