Answers

1. Contrary to value objects, entities have an identity.
2. No. The most important property of a value object is its immutability.
3. The entry-point object for any aggregate is called an aggregate root.
4. No, but objects from other domains and other hexagons can call domain services.
5. A policy is a pattern that encapsulates part of the problem domain knowledge in a block of code or an algorithm. A specification is a pattern that works with predicates to assert the validity of the properties of objects.
6. Because a POJO doesn’t depend on external technology details, such as a feature provided by an external library or a framework. Instead, a POJO relies only on a standard Java API, which makes POJOs simple and easy-to-reuse objects. POJOs are helpful for creating business rules objects that aren’t blurred by technology details.