Problems, Bad Database
Below you see a database with three tables.
This database has been badly designed.
Each table has a number of problems.
Table Subscription
| City |
Name |
Newspaper |
Publisher |
| Gouda |
HJ Nootenboom |
Automatisering Gids |
Stam |
| Gouda |
H.J Nootenboom |
Computable |
VNU |
| Zevenhoven |
S Peuskens |
Computable |
Stam |
Problems of the table Subscription
- The publisher of the newspaper Computable is ambiguous (polyinterpretable).
For one reader it's Stam, for another one it's VNU.
- One and the same reader is registered with different spellings in the adminstration.
Delivery Address
| Name |
Postcode |
Newspaper |
Address |
| HJ Nootenboom |
2803 DA |
Autom. Gids |
Groenhovenweg 43 |
| H.J. Nootenboom |
12345ABC |
Computable |
Groenh. weg 43-II |
Problems of the table Delivery Address
- The postcode 12345ABC is wrong, does not even match the Dutch format.
But there is no way to check the correctness of a postcode.
- The address of one reader is recorded twice.
That is not just cumbersome when the reader moves (dubble update), but it is unclear which one is the right version.
- The subscription of S Peuskens to Computable lacks address data.
Invoice Data
| Price |
Birthdate |
Name |
Postcode |
City |
| 75.00 |
32 sep 1951 |
Henk Jan Nootenboom |
00000 HHH |
Juinen |
| 0.00 |
01-04-1572 |
Stefan Peuskens |
2435xh |
Z. Hoven |
Problems of the table Invoice Data
- It's impossible to relate invoice data and subscriptions.
It's unclear which price is valid for a which newspaper.
Somebody can get an invoice bill, without subscription, or vice versa.
There isn't a good
foreign key.
- The postcode and city of Henk Jan Nootenboom are not existent in the Netherlands.
The invoice will never arrive.
It's impossible for the computer to get the address data from a different
table, as a result of a slightly different spelling of the name.
- Stefan Peuskens will get a invoice of 0 guilders, but will not receive a newspaper,
as the delivery address is unknown.
Could it be that this € 0,- has some special meaning and as a result there will be no invoice sent, and no newspaper delivered?
- The column birhtdate is irrelevant, is outside the scope.
The dates 01-04-1572 and 32 Sep 1951 are not reliable, probably specified wronly on purpose.
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