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DBMS 5NF

By Chaitanya Singh | Filed Under: DBMS

A relation is said to be in 5NF, if it satisfies the following conditions:

  • It is in 4NF.
  • It cannot be further broken down to smaller tables.
  • The decomposed tables join operation must be lossless, which means the decomposed tables joined using natural join should produce original relation without loosing any information.

5NF Example

Consider this table, a same course can be assigned to different teachers.

Stu_NameStu_CourseStu_Professor
RamC++Smith
RamJavaPaul
ShyamJavaPaul
ShyamDBMSTom
ShyamC++Robert

The problem with this relation is that all three columns combine together form a primary key. If you want to add a new course to the table, the Stu_Name and Stu_Professor fields are empty (null), which is not acceptable as they are part of primary key.

This relation is not in 5NF as it contains redundant data and it can be broken down to smaller tables.

Let’s break it down to three tables like this:

Table 1: Course

Stu_NameStu_Course
RamC++
RamJava
ShyamC++
ShyamDBMS
ShyamJava

Table 2: Professor

Stu_CourseStu_Professor
C++Smith
C++Robert
DBMSTom
JavaPaul

Table 3: Teaches

Stu_NameStu_Professor
RamSmith
RamPaul
ShyamTom
ShyamPaul
ShyamRobert
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