The Java EE 5 Tutorial  Self-Referential Relationships  A self-
referential relationship is a relationship between relationship
fields in the same entity. Part has a field bomPart that has a
one-to-many relationship with the field parts, which is also in
Part. That is, a part can be made up of many parts, and each of
those parts has exactly one bill-of-material part.  The primary
key for Part is a compound primary key, a combination of the
partNumber and revision fields. It is mapped to the PARTNUMBER
and REVISION columns in the EJB_ORDER_PART table.  public Part
getBomPart() {     return bomPart; public Collection<Part>
getParts() {     return parts;