f2 TODO list:

- modify __setattr__() to handle correctly reference counter of "previous" values, DONE
- handle more correctly null values '?' in _validate() DONE
- write a O.delete() primitive, with triggers and destruction propagation.
  In fact, a C.exit(o) might be more appropriate.                       DONE
- validate correctly cardinalities in F2_Object.__setattr__() DONE
- define and write a way of declaring schemas (XML ?) DONE

class Employee (Person):
	name = String
	lastname = String
	manager = Person
	
or:


class Employee(Person):
	initial_schema = 
	   { nom : db.String,
	     prenom : db.String,
	     work_in : (db.Departement, N), # cardinality. maximum is given by
	     manager : db.Person }	
	     

- Essayer d'appliquer le coup du _p_changed = 1 aux r_f des attributs OFF. DONE !!!!!
- expand rules for Class naming (smart class names with schema names, ...)
