TNF, Third Normal Form

Remove non key dependencies.

Can you find any transitive dependencies in the data, irrespective of the key? Can you find a value for one data element if you know an other one? This is often the most difficult step of normalisation.
Street and City are dependent on Postcode
In the given example Street and City are transitive dependent on Postcode. For a given postcode there is only one street and city (this is true in the Netherlands, but not necessarely in your country.)

Make a new table for this dependency. Design in Third Normal Form

  1. Copy the new key to the new table.
  2. Mark the key with an *, as foreign key. (This comes in handy at technical optimisation, when you'll design indexes.)
  3. Draw a one-to-many relation between the new and the old table.
  4. Move the dependent data elements to the new table.