Why is the third normal form important

Less redundancy thanks to database normalization

In the database of the online shop, the invoice data are assigned to the attributes Invoice number (R.-Nr.), date, customer, Customer number (K.No.), address, Invoice item number (P. no.), items, Item number (Item no.), Number (no.) and price assigned. Each line of the table stands for one data record. Such a record is called a Tuple designated.

The database section shown above acts as a Example of abad database design. It is noticeable at first glance that the table has numerous redundancies. In addition, the value ranges in the columns customer and address contain multi-valued data. One speaks of a non-normalized database.

The main disadvantage of non-normalized databases is the increased memory requirement due to redundant values. In addition, attributes that contain multi-valued data are difficult to read out and relate to one another.

Example: Both customers in the database section listed above are based in Musterhausen. But since this information was not collected separately, the database cannot easily be filtered for customers from the same location.

In order to avoid duplicate and multi-valued value ranges, there are three consecutive ones within the framework of relational database models Normal forms has been developed.

A normal form is a defined target state. For each normal form, special requirements have been defined that must be met if this target state is to occur. A database corresponds to the 1st, 2nd or 3rd normal form if all the requirements for the respective normal form are met.