MRP Exception Message Number

I need to write an ABAP report which uses the details on the MD04 Stock Requirements List detail screen for those items which have an Exception Message number (10, 20,30 etc..). The screen shows this data is held in a structure called MDEZ. I have tried performance tracing and ABAP debugging but can't find the actual database table where this data is held.(I'm a newbie).

Can anyone help with the relevant table name or appropriate function module?