Class Diagram

Class diagrams show object-oriented structures — classes, their attributes and methods, and the relationships between them.

Minimal Example

{
  "type": "class",
  "classes": [
    { "id": "animal", "name": "Animal", "methods": ["speak()"] },
    { "id": "dog", "name": "Dog", "methods": ["speak()"] }
  ],
  "relationships": [
    { "from": "dog", "to": "animal", "type": "inheritance" }
  ]
}

Full Example

{
  "type": "class",
  "classes": [
    {
      "id": "user",
      "name": "User",
      "attributes": ["id: string", "email: string", "name: string"],
      "methods": ["updateProfile()", "changePassword()"]
    },
    {
      "id": "order",
      "name": "Order",
      "attributes": ["id: string", "total: number", "status: string"],
      "methods": ["cancel()", "refund()"]
    },
    {
      "id": "lineItem",
      "name": "LineItem",
      "attributes": ["productId: string", "quantity: number", "price: number"]
    },
    {
      "id": "payment",
      "name": "PaymentProcessor",
      "methods": ["charge(amount)", "refund(transactionId)"]
    }
  ],
  "relationships": [
    { "from": "user", "to": "order", "type": "association", "label": "places" },
    { "from": "order", "to": "lineItem", "type": "composition", "label": "contains" },
    { "from": "order", "to": "payment", "type": "dependency", "label": "uses" }
  ]
}

Classes

Each class needs a unique id and a name.

Field	Required	Description
`id`	Yes	Unique identifier — relationships reference this
`name`	Yes	Display name shown in the class header
`attributes`	No	Array of attribute strings (e.g., `"name: string"`)
`methods`	No	Array of method strings (e.g., `"save()"`)

{
  "id": "product",
  "name": "Product",
  "attributes": ["id: string", "price: number"],
  "methods": ["applyDiscount(percent)"]
}

Relationships

Each relationship connects two classes by their id.

Field	Required	Description
`from`	Yes	Source class `id`
`to`	Yes	Target class `id`
`type`	Yes	Relationship type (see below)
`label`	No	Text on the connector

Relationship Types

Type	Arrow	Use for
`"inheritance"`	Solid with hollow triangle	"is a" (extends)
`"realization"`	Dashed with hollow triangle	"implements" (interface)
`"composition"`	Solid with filled diamond	"owns" (lifecycle-bound)
`"aggregation"`	Solid with hollow diamond	"has" (independent lifecycle)
`"association"`	Solid line	General "uses" or "knows about"
`"dependency"`	Dashed line	Weak "depends on"

More Examples

Repository Pattern

{
  "type": "class",
  "classes": [
    {
      "id": "repo",
      "name": "UserRepository",
      "methods": ["findById(id)", "save(user)", "delete(id)"]
    },
    {
      "id": "iRepo",
      "name": "IRepository",
      "methods": ["findById(id)", "save(entity)", "delete(id)"]
    },
    {
      "id": "entity",
      "name": "User",
      "attributes": ["id: string", "email: string"]
    },
    {
      "id": "db",
      "name": "Database",
      "methods": ["query(sql)"]
    }
  ],
  "relationships": [
    { "from": "repo", "to": "iRepo", "type": "realization" },
    { "from": "repo", "to": "entity", "type": "association", "label": "manages" },
    { "from": "repo", "to": "db", "type": "dependency", "label": "queries" }
  ]
}

Observer Pattern

{
  "type": "class",
  "classes": [
    {
      "id": "subject",
      "name": "EventEmitter",
      "attributes": ["listeners: Map"],
      "methods": ["on(event, fn)", "emit(event, data)"]
    },
    {
      "id": "observer",
      "name": "Observer",
      "methods": ["update(data)"]
    },
    {
      "id": "logger",
      "name": "Logger",
      "methods": ["update(data)"]
    },
    {
      "id": "metrics",
      "name": "MetricsCollector",
      "methods": ["update(data)"]
    }
  ],
  "relationships": [
    { "from": "subject", "to": "observer", "type": "aggregation", "label": "notifies" },
    { "from": "logger", "to": "observer", "type": "realization" },
    { "from": "metrics", "to": "observer", "type": "realization" }
  ]
}

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