If your problem is simply implementing the barcode functionality into existing procedures, then you need merely to add the field to the dictionary / data file and update all modules and procedures as normal.
Whether the barcode input is by means of keyboard or scanner is irrelevent; it is simply input as data by either device.
Typically, you need a field to take maximum 13 digits (there are various barcode schemes, but 13 digit UPC scheme is most commonly used in Europe).
If your client is producing products that need to have barcodes / UPC's assigned, you would need to register with your Spanish controlling body to get an allocated manufacturer code. The scheme is made up as follows, if I remember correctly, AABBBBXXXXXXZ, where AA=Country, BBBB=Manufacturer, XXXXXX = product code and Z = check digit, whose algorithm I have definitely forgotten! However, your local body will confirm this for you. Do provide for validation of the check digit on this field, as there will inevitably be keyboard input. I have seen, on many occassions, merchandise that has been barcoded by the producer with invalid UPC's because of no validation. This ends up being a disaster because most end users do validation and they would mostly reject and return products with incorrect codes.
Also see this link for Clarion addons
and this for specifically barcode support within clarion
Hope this helps.
Clive
clive@digitalsky.co.za