Fifth Normal Form (5NF)

The Fifth normal form (5NF) is generally not implemented in real-life database design. But we must learn the concept of it.

A relation will be in 5NF if

  • It is in 4NF
  • It does not hold any join dependency.
  • 5NF is also known as Project join normal form (PJ/NF).

Join Dependency

If a table holds the join dependency then

  • Decomposition of that table into multiple tables and re-joining of tables will always be the same table as before decomposition. It is also called lossless decomposition.

If a table does not hold the join dependency then

  • The result of Decomposition or rejoining, after decomposition, leads toward either loss of data or new entries, which are created in the table. It is called lossy decomposition.

Concept of 5th Normal Form

  • We can understand the 5th NF by understanding either joining dependency or breaking down the tables into parts and rejoining.
  • As Join dependency is a little bit of a confusing topic, let’s understand the breakdown of the tables into parts.

Suppose a table SPC with composite primary key {Supplier, product, customer}

In the above table, the supplier supplies products, and the customer can use these products, but note that the supplier does not directly supply to any customer.

In simple words, the Supplier (“Ali”) produces (“ABC”), and the Customer (“Nauman”) can use it. But Ali and Nauman are not directly connected.

Decomposition

After the Decomposition of the table (SPC) into three parts, as given below

Note that, In table (SC), the Supplier and Customer are directly connected. So, values are changed after the decomposition of the table (SPC) into parts.

So, the above table is in 5NF.