I have a question about the example presented in the Hibernate docs at http://www.hibernate.org/hib_docs/v3/reference/en/html/example-parentchild.html (section 21.2)

In this example of a Parent-Child relationship, the Child entity is required to contain a reference to the Parent. My question is why this is needed: the parent contains in the <set> mapping the column used as the key in the child table, and the Parent object created contains references to the child objects. It seems to me Hibernate has all the necessary information to persist the child without requiring it have a reference to its Parent.

Is it possible to create a mapping that has no reference from the child to the parent, where the ID field for the child is contained only in the Parent's collection? (Would a map rather than a set allow this?)