Refine the Fields
After you make a first stab at putting fields in tables, the next step is to refine your fields. A few classic slip-ups in creating fields are easily noticed. I prefer “slip-ups” instead of “mistakes” or “blunders” because they initially appear to be perfectly logical solutions to the database problems you face. But they violate database principles and will vastly reduce the effectiveness of your database.
No value in a table should depend on any other value in the table for its own value. This basic principle of database design might seem to offer more confusion than enlightenment. Perhaps this restatement will make things a little clearer: You must be able to change the value of any field without affecting ...