A self-referential relationship occurs between relationship fields in the same entity. Part has a field, bomPart, which 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. This key is mapped to the PARTNUMBER and REVISION columns in the EJB_ORDER_PART table:
... @ManyToOne @JoinColumns({ @JoinColumn(name="BOMPARTNUMBER", referencedColumnName="PARTNUMBER"), @JoinColumn(name="BOMREVISION", referencedColumnName="REVISION") }) public Part getBomPart() { return bomPart; } ... @OneToMany(mappedBy="bomPart") public Collection<Part> getParts() { return parts; } ...