how to find transparant table

Hi guru, need some help.

I know a little bit ABAP, and I got problem to find the table name.

I want to know what is the transparan table and field name

for item category :

SPRO->Materials Management->Purchasing->Define External Representation of Item Categories

then select itmCat(int) = 1, itmCat(ext)=B, text item category=Limit

select detail than at button Invoice receipt and field PO Item linked

if i click on PO item link and press help and see technical information , system

give me only : struct. RM06C, field : EBLAN, and Data element RBLAN,

when I tried to where-use-list EBLAN or RBLAN, but I did not get the

transparant table,

somebody can help where do the information were save ?

I mean what table are they using ?

thank you a lot.