PlantUML Class Diagram: Domain Modeling

Domain-Driven Design Models in PlantUML

Domain modeling is where class diagrams shine. PlantUML's stereotype and packaging features map directly to DDD tactical patterns.

Defining Aggregates

@startuml
package "Order Aggregate" <<Rectangle>> {
  class Order <<Aggregate Root>> {
    -orderId: OrderId
    -status: OrderStatus
    -items: List<OrderItem>
    +addItem(product, qty): void
    +submit(): void
    +cancel(): void
  }

  class OrderItem <<Entity>> {
    -lineId: LineId
    -productId: ProductId
    -quantity: int
    -unitPrice: Money
    +subtotal(): Money
  }

  class Money <<Value Object>> {
    -amount: BigDecimal
    -currency: Currency
    +add(other: Money): Money
    +multiply(factor: int): Money
  }

  Order *-- OrderItem
  OrderItem *-- Money
}
@enduml

Stereotypes

Use <<Aggregate Root>>, <<Entity>>, <<Value Object>>, and <<Domain Event>> stereotypes to label DDD building blocks. PlantUML renders stereotypes in guillemets above the class name.

Domain Events

class OrderSubmitted <<Domain Event>> {
  -orderId: OrderId
  -submittedAt: DateTime
  -totalAmount: Money
}

Order ..> OrderSubmitted : publishes

Bounded Context Boundaries

package "Order Context" {
  class Order
  class OrderItem
}

package "Inventory Context" {
  class Product
  class StockLevel
}

Order ..> Product : references by ID only

The package boundaries visualize bounded context separation. Cross-context references should only use IDs, never direct object references — the dashed dependency arrow with a note makes this constraint explicit.

Color Coding

skinparam class {
  BackgroundColor<<Aggregate Root>> LightBlue
  BackgroundColor<<Entity>> LightGreen
  BackgroundColor<<Value Object>> LightYellow
}

Using skinparam to color-code DDD building blocks makes large domain models much easier to scan.