The Universal Relation theory says that one attribute name in the model should map to only one concept. This means you cannot have an attribute called ‘Name’ for the Customer and another attribute called ‘Name’ for the Supplier. The first one needs to be called ‘CustomerName’ and the second one ‘SupplierName’.

Some background about this can be found in Jeffrey Ullman’s Stanford page in http://www-db.stanford.edu/~ullman/cs345notes/slides01-5.pdf