Third 3rd normal form, transitive dependency, Example of the third normal form in database systems

Third 3rd normal form, transitive dependency, Example of the third normal form in database systems

In this tutorial, we will learn about the followings;

  1. third 3rd normal form in a database system
  2. transitive dependency
  3. Example of the third normal form

What is a third normal form?

A database table is in 3rd normal form if the following two conditions are true;

  1. A database table is in second normal form and in first normal form.
  2. There is no transitive dependency.

What is a transitive dependency?

A transitive dependency is an indirect dependency.

What is an example of transitive dependency?

For example;

  • X depends on Y
  • Y depends on Z
  • So we can say that X depends on Z

Example of a third normal form:

FurnitureID CategoryID CategoryType Price
1 34 Tables 700$
2 76 Chair 500$

Table 1: Without Normalization

Primary key: Suppose Primary key is on FurnitureID.


There is a problem in this table because CategoryType is transitively depended on furniture ID. We can explain it according to the rule discussed above;

  • CategoryType depends on Category
  • CategoryID depends on FurnitureID
  •  So we can say that CategoryType depends on FurnitureID. This kind of dependency is a transitive dependency.


FurnitureID CategoryID Price
1 34 700$
2 76 500$

Table 2: Furniture

CategoryID Price
34 700$
76 500$

Table 3: Category

Table 2 and 3 demonstrates table conversion into the 3rd  Normal form

Primary key: Primary key is on FurnitureID and CategoryID.

Now the table is in 3rd normal form because all the table is in 2nd normal form and there is no transitive dependency.


Test Your Understandings

1.If there exist transitive dependency, then the database is in 3rd normal form?

Answer - Click Here:

2. Dependency shown below is the transitive dependency? Yes, No

X depends on Y,

Y depends on Z.

Z depends on Y.

Answer - Click Here:

Fazal Rehman Shamil
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