Diagrams¶

Diagrams help to communicate complex relationships and interconnections between different technical components, and are a great addition to project documentation. Zensical integrates with Mermaid.js, a very popular and flexible solution for drawing diagrams.

Configuration¶

This configuration enables native support for Mermaid.js diagrams. Zensical will automatically initialize the JavaScript runtime when a page includes a mermaid code block:

[project.markdown_extensions.pymdownx.superfences.custom_fences]
name = "mermaid"
class = "mermaid"
format = "pymdownx.superfences.fence_code_format"

markdown_extensions:
  - pymdownx.superfences:
      custom_fences:
        - name: mermaid
          class: mermaid
          format: !!python/name:pymdownx.superfences.fence_code_format

No further configuration is necessary. Advantages over a custom integration:

• Works with instant navigation without any additional effort
• Diagrams automatically use fonts and colors defined in the configuration¹
• Fonts and colors can be customized with additional style sheets
• Support for both, light and dark color schemes – try it on this page!

Usage¶

Use flowcharts¶

Flowcharts are diagrams that represent workflows or processes. The steps are rendered as nodes of various kinds and are connected by edges, describing the necessary order of steps:

``` mermaid
graph LR
  A[Start] --> B{Error?};
  B -->|Yes| C[Hmm...];
  C --> D[Debug];
  D --> B;
  B ---->|No| E[Yay!];
```

graph LR
  A[Start] --> B{Error?};
  B -->|Yes| C[Hmm...];
  C --> D[Debug];
  D --> B;
  B ---->|No| E[Yay!];

Use sequence diagrams¶

Sequence diagrams describe a specific scenario as sequential interactions between multiple objects or actors, including the messages that are exchanged between those actors:

``` mermaid
sequenceDiagram
  autonumber
  Alice->>John: Hello John, how are you?
  loop Healthcheck
      John->>John: Fight against hypochondria
  end
  Note right of John: Rational thoughts!
  John-->>Alice: Great!
  John->>Bob: How about you?
  Bob-->>John: Jolly good!
```

sequenceDiagram
  autonumber
  Alice->>John: Hello John, how are you?
  loop Healthcheck
      John->>John: Fight against hypochondria
  end
  Note right of John: Rational thoughts!
  John-->>Alice: Great!
  John->>Bob: How about you?
  Bob-->>John: Jolly good!

Use state diagrams¶

State diagrams are a great tool to describe the behavior of a system, decomposing it into a finite number of states, and transitions between those states:

``` mermaid
stateDiagram-v2
  state fork_state <<fork>>
    [*] --> fork_state
    fork_state --> State2
    fork_state --> State3

    state join_state <<join>>
    State2 --> join_state
    State3 --> join_state
    join_state --> State4
    State4 --> [*]
```

stateDiagram-v2
  state fork_state <<fork>>
    [*] --> fork_state
    fork_state --> State2
    fork_state --> State3

    state join_state <<join>>
    State2 --> join_state
    State3 --> join_state
    join_state --> State4
    State4 --> [*]

Use class diagrams¶

Class diagrams are central to object oriented programming, describing the structure of a system by modelling entities as classes and relationships between them:

``` mermaid
classDiagram
  Person <|-- Student
  Person <|-- Professor
  Person : +String name
  Person : +String phoneNumber
  Person : +String emailAddress
  Person: +purchaseParkingPass()
  Address "1" <-- "0..1" Person:lives at
  class Student{
    +int studentNumber
    +int averageMark
    +isEligibleToEnrol()
    +getSeminarsTaken()
  }
  class Professor{
    +int salary
  }
  class Address{
    +String street
    +String city
    +String state
    +int postalCode
    +String country
    -validate()
    +outputAsLabel()
  }
```

classDiagram
  Person <|-- Student
  Person <|-- Professor
  Person : +String name
  Person : +String phoneNumber
  Person : +String emailAddress
  Person: +purchaseParkingPass()
  Address "1" <-- "0..1" Person:lives at
  class Student{
    +int studentNumber
    +int averageMark
    +isEligibleToEnrol()
    +getSeminarsTaken()
  }
  class Professor{
    +int salary
  }
  class Address{
    +String street
    +String city
    +String state
    +int postalCode
    +String country
    -validate()
    +outputAsLabel()
  }

Use entity-relationship diagrams¶

An entity-relationship diagram is composed of entity types and specifies relationships that exist between entities. It describes inter-related things in a specific domain of knowledge:

``` mermaid
erDiagram
  CUSTOMER ||--o{ ORDER : places
  ORDER ||--|{ LINE-ITEM : contains
  LINE-ITEM {
    string name
    int pricePerUnit
  }
  CUSTOMER }|..|{ DELIVERY-ADDRESS : uses
```

erDiagram
  CUSTOMER ||--o{ ORDER : places
  ORDER ||--|{ LINE-ITEM : contains
  LINE-ITEM {
    string name
    int pricePerUnit
  }
  CUSTOMER }|..|{ DELIVERY-ADDRESS : uses

Other diagram types¶

Besides the diagram types listed above, Mermaid.js provides support for pie charts, gantt charts, user journeys, git graphs and requirement diagrams, all of which are not officially supported by Zensical. Those diagrams should still work as advertised by Mermaid.js, but we don't consider them a good choice, mostly as they don't work well on mobile.

Customization¶

If you want to customize Mermaid.js, e.g. to bring in support for ELK layouts, you can do so by adding a custom JavaScript file to your configuration:

import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.esm.min.mjs';
import elkLayouts from 'https://cdn.jsdelivr.net/npm/@mermaid-js/layout-elk@0/dist/mermaid-layout-elk.esm.min.mjs';

mermaid.registerLayoutLoaders(elkLayouts);
mermaid.initialize({
  startOnLoad: false,
  securityLevel: "loose",
  layout: "elk",
});

// Important: necessary to make it visible to Zensical
window.mermaid = mermaid;

[project]
extra_javascript = ["javascripts/mermaid.mjs"]

extra_javascript:
  - javascripts/mermaid.mjs