Does JBoss Rules engine (Drools) only support flat models as rule facts?

Issue

• Several documentations show JBoss Rules (Business Rule Engine) linking different objects by attributes instead of navigating by the object graph. Is this strategy, using flat models, a recommended way to work with BRMS?
• In BRMS 5.x releases the best practice was to create flat objects and link them by their id in the rules, for example.

public class Person{
  private int id;
}

public class Address{
private int id;

private int personId;
}

rule "old reccomendation rule"
when
    $person: Person()
        $address: Address(personId=$person.id)
then    
...
end

Does this still remain the best practice in BRMS 6.1 or should users use classes like this?

public class Person{
  private int id;
  private addresses ArrayList<Address>()
}