Due to the lack of following mechanisms, DBA generally do mistakes to maintain data quality:
- Use of NULL- e.g. a customer's contact number is null. It is very difficult to know whether the customer has no contact number or has never been asked to give their contact number.
- Referential Integrity: e.g. an orders inventory with an order allocated to customer number C0010, where that customer does not appear within the customer inventory.
- Value checking for reasonableness: e.g. customer's date of birth is 12/12/1850.
- Values constrained to a pre-defined domain – e.g. a user is adding record can add a customer title of ‘test' instead of selecting from a list of pre-defined values like Mr, Mrs, Dr etc.