1. Normalization of Database Tables
CHAPTER 4 1

2. Chapter Objectives Understand concepts of normalization
Learn how to normalize tables
Understand normalization and database design issues 2

3. Database Tables and Normalization
Normalization is a process for assigning attributes to entities.
It reduces data redundancies.
An un-normalized relation (table) stores redundant data, which can cause insertion, deletion, and modification anomalies.
In simple words: Normalization means keeping a single copy of data in your database.
Normalization theory provides a step by step method to remove redundant data and undesirable table structures. 4

4. Normal Forms
Tables are normalized by applying rules to create a series of normal forms:
First normal form (1NF)
Second normal form (2NF)
Third normal form (3NF)
Boyce/Codd normal form (BCNF)
Fourth normal form (4NF)
Projection Join normal form (PJNF, aka 5NF)
A table or relation in a higher level normal form always confirms to lower level normal forms.

5. Normal Forms
PJ/NF (5NF) Relations
4NF Relations
BCNF Relations
3NF Relations
2NF Relations
1NF Relations
While higher level normal forms are available, normalization up to BCNF is often found to be adequate for business data.

6. First Normal Form
A relation is in 1NF if all underlying domains contain atomic values only, i.e., the intersection of each row and column contains one and only one value.
The relation must not contain repeating groups.
PNo PName ENo EName Jcode ChgHr Hrs
1 Alpha 101 John Doe NE $65 20
105 Jane Vo SA $80 15
110 Bob Lund CP $60 40
2 Beta 101 John Doe NE $65 20
108 Jeb Lee NE $65 15
106 Sara Lee SA $80 20
3 Omega 102 Beth Reed PM $125 20
105 Jane Vo SA $80 10
Is the above relation in 1NF? 9

7. First Normal Form
The previous relation can be converted into first normal form by adding Pno and Pname to each row.
PNo PName ENo EName Jcode ChgHr Hrs
1 Alpha 101 John Doe NE $65 20
1 Alpha 105 Jane Vo SA $80 15
1 Alpha 110 Bob Lund CP $60 40
2 Beta 101 John Doe NE $65 20
2 Beta 108 Jeb Lee NE $65 15
2 Beta 106 Sara Lee SA $80 20
3 Omega 102 Beth Reed PM $125 20
3 Omega 105 Jane Vo SA $80 10
What is the primary key in this relation?
Do you see redundant data in this table?
What anomalies could be caused?

8. Functional Dependency Revisited
If A and B are attributes (or group of attributes) of a relation R, B is functionally dependent on A (denoted A B), if each value of A in R is associated with exactly one value of B in R.
A is called a determinant.
Consider the relation
Student (ID, Name, Soc Sec Nbr, Major, Deptmt)
Assume a department offers several majors, e.g. INSY department offers, INSY, MASI, and POMA majors.
How many determinants can you identify in Student?

9. Functional Dependency Revisited
A Dependency diagram ID
Name
Soc_Sec_Nbr
Major
Dept

10. Functional Dependency Revisited
Full functional dependency
Attribute B is fully functionally dependent on attribute A if it is functionally dependent on A and not functionally dependent on any proper subset of A.
This becomes an issue only with composite keys.
Transitive dependency
A, B and C are attributes of a relation such that A B and B C, then C is transitively dependent on A via B (provided that A is not functionally dependent on B or C)

11. Second Normal Form Dependency diagram for Project PNo PName ENo EName
JCode
ChgHr
Hrs

12. Second Normal Form A relation is in 2NF if: It is in 1NF and
every nonkey attribute is fully dependent on the primary key, i.e., no partial dependency.
A nonkey attribute is one that is not a primary key or part of a primary key.
We create new relations that are in 2NF through projection of the original relation.
Project(PNo, PName)
Employee(ENo, EName, Jcode, ChgHr)
Charge(PNo, ENo, Hrs) 14

13. 2NF
2NF
PNo
PName
ENo
EName
JCode
ChgHr
PNo
ENo
Hrs

14. Second Normal Form Tables in 2NF Charge PNo ENo Hrs 1 101 20 Project
Project
PNo PName
1 Alpha
2 Beta
3 Omega
Employee
ENo EName JCode ChgHr
101 John Doe NE $65
102 Beth Reed PM $125
105 Jane Vo SA $80
106 Sara Lee SA $80
108 Jeb Lee NE $65
110 Bob Lund CP $60

15. Second Normal Form
Note that the original relation can be recreated through natural join of the new relation.
Thus, no information is lost in the process of creating 2NF relations from a 1NF relation. This is called nonloss decomposition.
If a relation that is in 1NF has a non composite primary key (i.e., the primary key consists of a single attribute) what can you say about its status with regard to 2NF?
Do you see any redundant data in the tables that are in 2NF?
What anomalies could be caused by such redundancy?

16. Third Normal Form A relation is in 3NF if: It is in 2NF and
every nonkey attribute is nontransitively dependent on the primary key (i.e., no transitive dependency).
Relation Employee has a transitive dependency:
ENo JCode ChgHr
Employee can be replaced by two relations, that are in 3NF:
Employee(ENo, EName, Jcode)
Job(JCode, ChgHr) 16

17. 3NF
3NF
PNo
PName
JCode
ChgHr
ENo
EName
JCode
PNo
ENo
Hrs

18. Third Normal Form Tables in 3NF Charge PNo ENo Hrs 1 101 20 Project
Project
PNo PName
1 Alpha
2 Beta
3 Omega
Employee
ENo EName Jcode
101 John Doe NE
102 Beth Reed PM
105 Jane Vo SA
106 Sara Lee SA
108 Jeb Lee NE
110 Bob Lund CP
Job
Jcode ChgHr
CP $60
NE $65
PM $125
SA $80

19. Boyce-Codd Normal Form
A relation is in BCNF if
every determinant is a candidate key.
A determinant is an attribute (combination of attributes) on which some other attribute is fully functionally dependent.
BCNF is a special case of 3NF.
The potential to violate BCNF may occur in a relation that:
contains two (or more) composite candidate keys,
these keys overlap and share at least one attribute.
Thus, if a table contains only one candidate key or only non-composite keys, then 3NF and BCNF are equivalent. 18

20. 3NF Table Not in BCNF
Figure 4.7

21. Decomposition of Table Structure to Meet BCNF
Figure 4.8

22. Boyce-Codd Normal Form
Consider the following example:
The members of a recruiting team interview candidates on a one-to-one basis. Each member is assigned a particular room on a given date. Each candidate is interviewed only once on a specific date. He/she may return for follow up interviews on later dates.
Interview (CID, IDate, ITime, StaffID, RmNo)
CID IDate ITime StaffID RmNo
C :00 S01 B107
C :00 S01 B107
C :00 S05 B108
C :00 S06 B108

23. Boyce-Codd Normal Form
This relation has following functional dependencies:
CID, IDate ITime, StaffID, RmNo
StaffID, IDate, ITime CID, RmNo
RmNo, Idate, Itime StaffID, CID
StaffID, IDate RmNo
This relation does not have any partial or transitive dependencies on the primary key (CID, IDate)
It is not in BCNF because (StaffID, Idate) is a determinant but not a candidate key.
The new relations in BCNF are:
Interview (CID, IDate, ITime, StaffID)
Room(StaffID, IDate, RmNo)

24. Dependency Diagram Fig 1 Fig 2 Fig 3 CID IDate ITime StaffID RmNo CID

25. Fourth Normal Form A table is in 4NF if
it is in 3NF and
has no multiple sets of multivalued dependencies.
Consider the following example:
Each course is taught by many teachers and requires many texts.
CTXU (Unnormalized)
Course Teacher Text
Physics Green Basic Mechanics
Brown Intro to Optics
Math White Modern Algebra
Intro to Calculus
CTXN (Normalized)
Course Teacher Text
Physics Green Basic Mechanics
Physics Green Intro to Optics
Physics Brown Basic Mechanics
Physics Brown Intro to Optics
Math White Modern Algebra
Math White Intro to Calculus 30

26. Fourth Normal Form
CTXN is in BCNF, because it is all key and there are no other functional dependencies.
It, however, has redundant data that could cause update anomalies.
This table shows two multivalued dependencies:
Each course has a defined set of teachers and
Course Teacher
Each course has a defined set of textbooks.
Course Text
MVDs can exist only when the relation has at least three attributes.
An FD is a special case of MVD when the set of dependent values has a single value.

27. Fourth Normal Form Tables in 4NF CX CT Course Text Course Teacher
Physics Green
Physics Brown
Math White CX
Course Text
Physics Basic Mechanics
Physics Intro to Optics
Math Modern Algebra
Math Intro to Calculus

28. Conversion to 4NF Figure 4.15 Set of Tables in 4NF Figure 4.14
Multivalued Dependencies

29. Normalization and Database Design
Normalization should be part of the design process
E-R Diagram provides macro view
Normalization provides micro view of entities
Focuses on characteristics of specific entities
May yield additional entities
Difficult to separate normalization from E-R diagramming
Business rules must be determined
Normalization purity is difficult to sustain due to conflict in:
Design efficiency
Information requirements
Processing

30. Denormalization
Normalized (decomposed) tables require additional processing, thus reducing system speed.
Sometimes normalization is not done keeping in mind processing speed requirements and practical aspects of the situation.
A good example is: storing Zip code and City as attributes in a Customer relation violates 3NF because City is transitively dependent on Cust ID via Zip Code.
Why should we not create a separate relation ZIP (ZipCode, City)? 32