concept Entity > NamedConcept {
}

abstract concept AbstractJavaObjectEntity<A> > Entity {
  abstract A object();
}

concept TransientJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {
  gettable transient A object;
}

concept PersistentJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {
  gettable A object;
}

concept ConceptEntity<A extends Concept> extends AbstractJavaObjectEntity<A> {
  new Ref<A> concept;
  
  A object() { ret concept!; }
}