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Fourth Normal Form (4NF)
What is 4NF?
The 4NF comes after 1NF, 2NF, 3NF, and Boyce-Codd Normal Form. It was introduced by Ronald Fagin in 1977.
To be in 4NF, a relation should be in Bouce-Codd Normal Form and may not contain more than one multi-valued attribute.
Example
Let us see an example −
<Movie>
Movie_Name | Shooting_Location | Listing |
MovieOne | UK | Comedy |
MovieOne | UK | Thriller |
MovieTwo | Australia | Action |
MovieTwo | Australia | Crime |
MovieThree | India | Drama |
The above is not in 4NF, since
- More than one movie can have the same listing
- Many shooting locations can have the same movie
Let us convert the above table in 4NF −
<Movie_Shooting>
Movie_Name | Shooting_Location |
MovieOne | UK |
MovieOne | UK |
MovieTwo | Australia |
MovieTwo | Australia |
MovieThree | India |
<Movie_Listing>
Movie_Name | Listing |
MovieOne | Comedy |
MovieOne | Thriller |
MovieTwo | Action |
MovieTwo | Crime |
MovieThree | Drama |
Now the violation is removed and the tables are in 4NF.
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