data reference

 hi all,

can any body tell me a little about adding more than one data reference 
to a display ? how do i connect two data references to one display ?

 DataReferenceImpl ref = new DataReferenceImpl("ref");
     DataReferenceImpl refx = new DataReferenceImpl("refx");
  final PickManipulationRendererJ3D pmr3d = new
PickManipulationRendererJ3D();
    ref.setData(field);
    refx.setData(fieldx);
    display.addReferences(pmr3d,ref);

thanks,

 isaac