1. Normalization
ACSC 425
Database Management Systems

2. Overview What is normalization? What are the normal forms?
How to normalize relations?

3. Introduction Question:
How many, and what, relations (tables) should be used to store my data?
Is the current relation free of problems?

4. Normalization
Normalization is a process of producing a set of related relations(tables) with desirable attributes, given the data requirements of a domain
The goal is to remove redundancy and other data modification (insertion, update and deletion) problems
Usually dividing a table into 2 or more tables
Using Normal Forms as a guide

5. Normal Forms Fewer abnomallies... Normalization …but more tables
Normal forms are guidelines (steps) for the normalization process
Fewer abnomallies...
Normalization
…but more tables
Unnormalized Form (UNF)
1st Normal Form (1NF)
2nd Normal Form (2NF)
3rd Normal Form (3NF)
Boyce Codd Normal Form (BC/NF)
4th Normal Form (4NF)
5th Normal Form
DK/NF

6. Normalization – 1NF A table is in 1NF if
it satisfies the definition of a relation
Review: what are the characteristics of a relation?
No “repeating groups” (columns)

7. Relation
A relation is a two-dimensional table that has specific characteristics:
The table consist of rows and columns
Rows contain data about entity instances
All values in a row describes the same entity instance
Columns contain data about attributes of the entity
All values in a column are of the same kind 7

8. Relation (continued) Relation’s specific characteristics go on:
Each row is distinct
A Cell of the table hold a single value
Each column has a unique name
The order of the rows is unimportant
The order of the columns is unimportant 8

9. Repeating Groups Customer ID First Name Surname Telephone Number 123
Robert
Ingram
456
Jane
Wright
789
Maria
Fernandez
Customer ID
First Name
Surname
Tel. No. 1
Tel. No. 2
Tel. No. 3
123
Robert
Ingram
456
Jane
Wright
789
Maria
Fernandez

10. Transforming to 1NF Transforming to rows, rather than columns
Customer ID
First Name
Surname
Telephone Number
123
Robert
Ingram
456
Jane
Wright
789
Maria
Fernandez

11. Transforming to 1NF: Example
Another example
UNF 1NF

12. Problems in 1NF
Basically has the same problem as the spreadsheet tables
Redundancy
Data may be inconsistent after modification

13. Non-Relation Examples
Single value
Column same kind, row describes the complete instance 13

14. Non-Relation Examples (2)
Emp_Name
Emp_Age
Emp_Phone
Emp_
Jordan Hail 45
Jack Parsons 28
Tom Jackson 23
Liz Marsten
Thirty
Single value
Column same kind, row describes the complete instance 14

15. Higher Normal Forms
Normal forms higher than 1NF deal with functional dependency
Identifying the normal form level by analyzing the functional dependency between attributes (fields)

16. Functional Dependency
If each value of attribute A is associated with only one value of attribute B, we say
A determines B
Or, B is dependent on A
Denoted as: A  B
Functional dependence describes relationships between attributes (not relations)
Note: A (or B) could be a set of fields

17. Functional Dependency Examples
For each SSN, there is only one corresponding first name (or last name), so:
SSN determines FirstName
SSN  FirstName
Non-dependency example
Each instructor teaches multiple courses, so:
InstructorId does not determines CourseNumber

18. Functional Dependency and Keys
By definition, a primary key (candidate key) functionally determines all other attributes
Primary key
Surrogate key
Composite primary key
Dependency diagram
ISBN
Title
PubDate
ListPrice

19. Functional Dependency Exercise
CustomerNum  CustomerName?
{Street, City, State}  Zip?
CustomerName  Balance?
State (?) Zip
RepNum ( ? ) CustomerName

20. Normalization – 2NF A relation is in 2NF, if Partial dependency A B C
It is in 1st normal formal, and
All nonkey attributes must be functionally dependent on the whole primary key (Full dependency)
No partial dependency
It implies that a relation is in 2NF if there is a single-attribute primary key (candidate key)
Partial dependency
A non-key attribute is dependent on part of a primary key A B C D

21. Transforming to 2NF A B C D A B C B D Identify primary key (PK)
If PK consists of only one field, then it is in 2NF
If PK is a composite key, then analyze functional dependency between part of primary key and other non-key attributes
Move partial dependency involved attribute to another relation A B C D A B C B D

22. A Relation in 1NF but Not in 2NF
Partial dependency

23. Transforming to 2NF: Example
Order
Order
Product
OrderItem

24. Problems in 2NF
Again, redundancy and potential inconsistency

25. Normalization – 3NF A relation is in 3NF, if Transitive dependency
It is in 2nd normal formal, and
All attributes must, and only, be functionally dependent on candidate keys
No transitive dependency
Transitive dependency
A  B and B  C, then A  C A B C D

26. A Relation in 2NF but Not in 3NF
Identify primary key (PK) and Look for transitive dependence
Transitive dependency

27. Transforming to 3NF
Move the attributes involved in transitive dependency to another relation
Order
Customer

28. Some Practical Tips
If there are attributes of two different entities in one table, there are usually problems
To identify the normalization level, determine the primary key first; then look for partial dependence and transitive dependence
Generally relations in the 3rd normalization forms are considered to be well formed; going higher may introduce unnecessary structural complexity which is inefficient for data queries
Very often tables can go for lower normal forms (de-normalization) depending on design requirements

29. Normalization Exercise 1-1
Which normal form is the above table in?
1NF
2NF
3NF
UNF

30. Normalization Exercise 1-2
Which normal form is the above table (2nd one) in?
1NF
2NF
3NF
UNF

31. Normalization Exercise 1-3
Which normal form is the above table (first one) in?
1NF
2NF
3NF
UNF

32. Normalization Exercise 1-4
Final database design with 3 tables

33. Summary

34. Summary
Key concepts
Normalization
Normal forms
Functional dependency