JPA Relationship Types
OneToOne - A unique reference from one object to another, inverse of a OneToOne.
ManyToOne - A reference from one object to another, inverse of a OneToMany.
OneToMany - A Collection or Map of objects, inverse of a ManyToOne.
ManyToMany - A Collection or Map of objects, inverse of a ManyToMany.
Embedded - A reference to a object that shares the same table of the parent.
ElementCollection - JPA 2.0, a Collection or Map of Basic or Embeddable objects, stored in a separate table.