What is the difference between COORDER (AUFNR) and CO_DOC_NO (BELNR) in the data source 0CO_OM_OPA_6

Hi,

What is the difference between COORDER (AUFNR) and CO_DOC_NO (BELNR) in the data source 0CO_OM_OPA_6?

And, how it is linked with Notifications (QMNUM)?

Actually, in the extraction on Data source 0CO_OM_OPA_6, the field QMNUM is appearing blank. Any clues will be helpful.

Regards,

Ravi