4th normal form, Boyce Codd normal form, Multi-valued dependency in database systems

4th normal form, Boyce Codd normal form, Multi-valued dependency in database systems

In this tutorial, we will learn about the followings;

  1. 4th normal form in database systems
  2. Boyce Codd normal form
  3. Multi-valued dependency

What is the 4th normal form?

A relation is in 4th normal form if following conditions are true;

  1. it is in Boyce coded normal form
  2. There should be no multi-valued dependency

What is Boyce Codd normal form?

A relation is in Boyce Codd normal form if and only if every determinant is a candidate key. Boyce Codd normal form is stronger than third normal form so it is also called 3.5 normal form.

Primary Key (Key attributes) Non-Key attributes
Project_ID Part_id Part_name  Quantity used
501 001 RAM 20
502 002 Hard disk 33
503 003 CPU 44

Table 1: Before Boyce Codd normal form

 

Primary Key (Key attributes) Non-Key attributes
Project_ID Part_id Quantity used
501 001 20
502 002 33
503 003 44
Primary Key (Key attributes) Non-Key attributes
Part_id Part_name 
001 RAM
002 Hard disk
003 CPU

Table 2,3: After converting into Boyce Codd normal form

What is a multi-valued dependency?

The multi-valued dependency exists when a relation has at least 3 attributes and 2 of them are multi-valued and their values depend on only the 3rd attribute.

Primary Key (Key attributes) Non-Key attributes
Employee_ID BPS interest
501 16 Cricket
501 16 Hockey
502 17 Hockey

 

 

 

 

 

Table 4: Before removing multi-valued dependencies

Primary Key (Key attributes) Non-Key attributes
Employee_ID BPS
501 16
502 17
Primary Key (Key attributes) Non-Key attributes
Employee_ID interest
501 Cricket
501 Hockey
502 Hockey

 

 

 

 

 

Table 5,6: After removing removing mutli-valued dependencies

Fazal Rehman Shamil
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