Fourth Normal Form (4NF)

Well we have already seen the Zero Normal Form (0NF), First Normal Form (1NF), Second Normal Form (2NF), and Third Normal Form (3NF) databases. Now I am going to try to explain and show an example of the Fourth Normal Form (4NF) database and explain even what Fifth Normal Form (5NF normalized database is.) Below is a rendition of the 2NF database from the last page normalized to (3NF) specifications.

PersonID (PK)	NameID	PlaceID	LocationID
1	1	1	1
2	2	2	1
3	3	3	3
4	4	4	4
5	5	5	4

NameID (PK)	FirstName	MiddleInitial	LastName
1	Joseph	P	Dimaggis
2	George	H	Ruth
3	Reginald	M	Jackson
4	Joseph		Torre
5	William		Martin

PlaceID (PK)	Address
1	123 foo lane
2	124 foo lane
3	125 foo lane
4	126 foo lane
5	127 foo lane

StudentID (PK)	PersonID (FK)	DepartmentID (FK)	ProfessorID (FK)
1	1	400	1
2	2	400	1
3	2	500	2

LocationID (PK)	Location	LocationType
1	43235	zip
2	Columbus	city
3	Ohio	state
4	10001	zip
5	Bronx	city
6	New York	state

ProfessorID (PK)	PersonID (FK)	DepartmentID (FK)
1	1	400
2	2	500

DepartmentID (PK)	Department (FK)
400	Computer Science
500	Math

Pieces of this database are 4NF, but not all of it. As you can see this is a great big mess and 5NF is even worse. These sorts of normalized databases can not be jus conjured up at will, but must be planned and have the necessary data for such a feat.

Updated: Mar. 22, 2005; Joe Gakenheimer