We can enhance the domain model with more rich information.
We will discuss how to show inheritance in order to show subtypes and how to provide more information to someone viewing the diagram with descriptions and multiplicity.
We might want to represent subclasses of Title:
classDiagram
Title -- Genre
Title *-- Season
Title *-- Review
Title o-- Actor
TV Show --|> Title
Short --|> Title
Film --|> Title
Season *-- Review
Season *-- Episode
%%Episode *-- Review
Generalization are defined using --|> and are rendered on the diagram as empty arrows.
One of the key features of a domain model written with UML is that you can describe how the entities interact with regard to their relationships.
In a lot of cases, a lot of the descriptions can be simply desscribed as has.
It is preferable to add more detailed description for relationships:
classDiagram
Title -- Genre: is associated with
Title *-- Season: has
Title *-- Review: has
Title o-- Actor: casts
TV Show --|> Title: implements
Short --|> Title: implements
Film --|> Title: implements
Viewer --> Title: watches
Season *-- Review: has
Season *-- Episode: contains
Episode *-- Review: has
The relationship between Viewer entity and Title entity is a directional association. This means Viewer holds a reference to Title, but Title doesn't hold a reference to Viewer.
Multiplicity describes how many of one type of entity relates to another. It allows us to define whether relationships are one-to-one, one-to-many, none-to-many, many-to-many, and everything in between.
classDiagram
Title "1..*" -- "1..*" Genre: is associated with
Title "1" *-- "0..*" Season: has
Title "1" *-- "0..*" Review: has
Title "0..*" o-- "1..*" Actor: casts
TV Show --|> Title: implements
Short --|> Title: implements
Film --|> Title: implements
Viewer "0..*" --> "0..*" Title: watches
Season "1" *-- "0..*" Review: has
Season "1" *-- "1..*" Episode: contains
Episode "1" *-- "0..*" Review: has
We can add a title to any Mermaid diagram simply by adding a block of code to the top of the markup. It must go at the very top, even above the diagram type definition.
---
title: Streamy Domain Model
---
classDiagram
Title "1..*" -- "1..*" Genre: is associated with
link Title "https://mermaid.js.org/syntax/classDiagram.html" _blank
Title "1" *-- "0..*" Season: has
Title "1" *-- "0..*" Review: has
Title "0..*" o-- "1..*" Actor: casts
TV Show --|> Title: implements
Short --|> Title: implements
Film --|> Title: implements
Viewer "0..*" --> "0..*" Title: watches
Season "1" *-- "0..*" Review: has
Season "1" *-- "1..*" Episode: contains
Episode "1" *-- "0..*" Review: has