I have two files (PO's & Invoices) each with its respective table data (PO_data & INV_data). From within the Invoice portal I would like to be able to enter "line number 1" and have it display the corresponding line number data (i.e Part No., Description, price, etc) from the PO file. Either displayed or copied via a lookup.

PO Key = PO_No_id

I cannot get the relationship right !!

Either displayed or copied via a lookup

Why? When you can have more than a single relational key in your items lines?

The lookups have a point in the offer when you're pulling an item from stock in a specific moment, if prices are likely change.

The next issue is that why have two files for the matter, when the content of the two documents have stunning redundance to exhibit? Only in larger organizations where brances have different task to do with the same data, could the separation model perhaps make some points - but here is it usually differences in the presentation layer, not the core data tables at hand, is this a from fm5-6 migrated solution?

--sd