unresolved

1. JPA
1. onetoone (targetentity)
1.  If we did, we would need to specify the type of entity that will be stored in the
   Collection that is needed by the persistence provider. The code is shown in Listing 4-21 and looks
   almost identical, except for the targetEntity element that indicates the entity type.
2. set vs list to guarantee the uniqueness of elements in collection
2. validation
3. cascade
4. domain modelling correction
5.