/**
  * Creates Primary Key.
  *
  * @param ref External Reference.
  * @param xref Castor XRef.
  */
 private void createPrimaryKey(ExternalReference ref, XrefType xref) {
   DbReferenceType primaryRef = new DbReferenceType();
   primaryRef.setDb(ref.getDatabase());
   primaryRef.setId(ref.getId());
   xref.setPrimaryRef(primaryRef);
 }
 /**
  * Creates Secondary Key.
  *
  * @param ref External Reference
  * @param xref Castro XRef.
  */
 private void createSecondaryKey(ExternalReference ref, XrefType xref) {
   DbReferenceType secondaryRef = new DbReferenceType();
   secondaryRef.setDb(ref.getDatabase());
   secondaryRef.setId(ref.getId());
   xref.getSecondaryRef().add(secondaryRef);
 }
 /**
  * Generates XRef Key.
  *
  * @param ref External Reference
  * @return Hash Key.
  */
 private String generateXRefKey(ExternalReference ref) {
   return ref.getDatabase() + "." + ref.getId();
 }