Domain-Driven Design — DDD Pattern Reference

Supporting skill providing DDD tactical and strategic pattern guidance for the microservice-designer harness.

Tactical Patterns Reference

Entity

An object defined by its identity that persists over time.

• Characteristics: Has unique identifier; mutable state; equality by ID not value
• Examples: Order, Customer, Product, Invoice
• Implementation: Generate stable ID at creation (UUID); never expose internal state directly; protect invariants via methods

Value Object

An object defined by its attributes with no conceptual identity.

• Characteristics: Immutable; equality by value; side-effect-free; replaceable
• Examples: Money(amount, currency), Address, EmailAddress, DateRange
• Implementation: Validate all fields in constructor; return new instance on transformation; share freely (no identity)