How does DDD relate to the SOLID principles?

DDD naturally supports SOLID, because both are built on separation of concerns and loose coupling:

1. S: Single Responsibility: each entity reflects one business concept.
2. O: Open/Closed: behavior is extended with new domain rules without breaking existing code.
3. L: Liskov Substitution: domain interfaces allow implementations (for example, repositories) to be substituted.
4. I: Interface Segregation: interfaces are small and reflect specific actions in the domain.
5. D: Dependency Inversion: the domain depends on abstractions, infrastructure depends on the domain.

Summary: DDD applies SOLID not to classes, but to the architecture of the business itself.