code: public void unlink(Object obj, ObjectReferenceDescriptor ord, boolean insert)
      {
         linkOrUnlink(false, obj, ord, insert);
      }
docs: Unlink the specified reference from this object.
  More info see OJB doc.
  
  @param obj Object with reference
  @param ord the ObjectReferenceDescriptor of the reference
  @param insert flag signals insert operation