An aggregate’s public interface is responsible for validating the input and enforcing all of the relevant business rules and invariants. This strict boundary also ensures that all business logic related to the aggregate is implemented in one place: the aggregate itself. This makes the application layer6 that orchestrates operations on aggregates rather simple:7 all it has to do is load the aggregate’s current state, execute the required action, persist the modified state, and return the operation’s result to the caller:
