Не могу понять Criteria API

Можете на простом языке объяснить для чего sessionFactory, CriteriaBuilder, CriteriaQuery, Root?

public List<Cities> getCitiesByCountry(Long id) {
    Session session = sessionFactory.openSession();
    CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
    CriteriaQuery<Cities> query = criteriaBuilder.createQuery(Cities.class);
    Root root = query.from(Cities.class);
    Predicate predicate = criteriaBuilder.equal(root.get("countries").get("id"), id);
    List<Cities> list = session.createQuery(query.where(predicate)).getResultList();
    return list;
}