Last updated on:September 24th, 2018,

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 the 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_IDPart_idPart_name Quantity used
501001RAM20
502002Hard disk33
503003CPU44

Table 1: Before Boyce Codd normal form

 

Primary Key (Key attributes)Non-Key attributes
Project_IDPart_idQuantity used
50100120
50200233
50300344
Primary Key (Key attributes)Non-Key attributes
Part_idPart_name 
001RAM
002Hard disk
003CPU

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_IDBPSinterest
50116Cricket
50116Hockey
50217Hockey

 

 

 

 

 

Table 4: Before removing multi-valued dependencies

Primary Key (Key attributes)Non-Key attributes
Employee_IDBPS
50116
50217
Primary Key (Key attributes)Non-Key attributes
Employee_IDinterest
501Cricket
501Hockey
502Hockey

 

Table 5,6: After removing mutli-valued dependencies

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2 thoughts on “4th normal form, Boyce Codd normal form, Multi-valued dependency in database systems

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