Based on your original post this is how I would organize / normalize:
tbl_major_companiesCompanyName (PRIMARY KEY - Cascade on update)
Precision
Dell
HP
CompanyID
13 digit number
13 digit number
13 digit number
tbl_subsidiariesSubsidiaryID (PRIMARY KEY - Cascade on update)
CompanyName (FOREIGN KEY)
Country
Britain
Italy
France
Germany
City
London
Milan
Paris
German City?
tbl_productsProductSerial (PRIMARY KEY - Cascade on update) changed ProductID to ProductSerial as more decriptive and less redundant (i.e. it is already unique)
ProductName
CompanyName (FOREIGN KEY) or SubsidiaryID (FOREIGN KEY) depending on how you track your data
The following is based on additional information you provided later on:
tbl_sellersSellerID (PRIMARY KEY - Cascade on update)
SellerName
SellerType I changed this from SellerUniqueLabel because it is not a unique label
SellerCountry I added this
SellerCity I added this
tbl_sales I added this table to join tbl_products and tbl_sellersSalesID (PRIMARY KEY - Cascade on update)
SellerID (FOREIGN KEY)
ProductSerial (FOREIGN KEY)
UnitCost
The tables are linked by the attributes with primary and foreign keys. Just be sure to set primary keys to cascade on update.