SNF, Second Normal Form
Remove part key dependencies
Are any data elements dependent on a part of the
- Create a new
table for these data elements,
avobe the old one.
Draw a connection between the old and the new table, a
many to one
- Mark the relation at the many side with a red capital
- The new table will get a smaller
Create new sticky pads for the new key.
Keep the key in the old table.
- Move the dependent data to the new table.
- Repeat these steps for the other part-key dependencies.
Note: In this old table there is no data anymore.
Yet, the combination of keys is meaningful.
Such a link table makes a many to many relation possible:
This is quite a reasonable
you can find related information in the other
- One reader can have many subscriptions to various newspapers.
- One newspaper has many readers with a subscription.
- Subscription has the tax number.
- With the tax number you can read the correct
- In the row of Reader there is oa the house address and the house number.