1. Chapter 5 Normalization of Database Tables
Database Systems: Design, Implementation, and Management
Peter Rob & Carlos Coronel

2. In this chapter, you will learn:
What normalization is and what role it plays in database design
About the normal forms 1NF, 2NF, 3NF, BCNF, and 4NF
How normal forms can be transformed from lower normal forms to higher normal forms
That normalization and E-R modeling are used concurrently to produce a good database design
That some situations require denormalization to generate information efficiently

3. Database Tables and Normalization
Normalization is a process for assigning attributes to entities. It
reduces data redundancies
helps eliminate data anomalies.
produces controlled redundancies to link tables
Normalization works through a series of stages called normal forms:
First normal form (1NF)
Second normal form (2NF)
Third normal form (3NF)
Fourth normal form (4NF)
The highest level of normalization is not always desirable.

4. Database Tables and Normalization
The Need for Normalization
Case of a Construction Company
Building project -- Project number, Name, Employees assigned to the project.
Employee -- Employee number, Name, Job classification
The company charges its clients by billing the hours spent on each project. The hourly billing rate is dependent on the employee’s position.
Periodically, a report is generated. Table 5.1
The easiest way to generate the required report might seem to be a table whose contents correspond to the reporting requirements. Figure 5.1

7. Database Tables and Normalization
Need for Normalization: Problems with the Figure 5.1
The project number is intended to be a primary key, but it contains nulls.
The table displays data redundancies.
The table entries invite data inconsistencies.
The data redundancies yield the following anomalies:
Update anomalies. (modify JOB_CLASS for Employee 105)
Insertion anomalies. (a new Employee not yet assigned)
Deletion anomalies. ( Employee 103 quits)

8. Database Tables and Normalization
Conversion to 1NF
Repeating groups – a group of multiple entries can exist for any single key attribute occurrence.
Repeating groups must be eliminated Any project number (PROJ_NUM) can have a group of several data entries.
A relational table must not contain repeating groups.

9. Step 2: Identify the Primary Key
Step 1: Eliminate the Repeating Groups – Repeating groups can be eliminated by adding the appropriate entry in at least the primary key column(s).
Step 2: Identify the Primary Key
Uniquely identifies attribute values (rows)
Combination of PROJ_NUM and EMP_NUM

10. Database Tables and Normalization
Step 3: Identify all Dependencies
Dependency Diagram
The primary key components are bold, underlined, and shaded in a different color.
The arrows above entities indicate all desirable dependencies ( dependencies based on PK )
The arrows below the dependency diagram indicate less desirable dependencies –
partial dependencies ( dependencies based on only a part of PK )
transitive dependencies ( nonprime attribute → nonprime attribute )
Prime attribute = Key attribute
Nonprime attribute = Nonkey attribute

11. Database Tables and Normalization
EMP_NUM → EMP_NAME, JOB_CLASS_, CHG_HOUR
PROJ_NUM → PROJ_NAME
JOB_CLASS → CHG_HOUR

12. Database Tables and Normalization
1NF Definition
The term first normal form (1NF) describes the tabular format in which:
All the key attributes are defined.
There are no repeating groups in the table. Each row/col intersection can contain one and only one value, not set of values.
All attributes are dependent on the primary key.
All relational tables satisfy the 1NF requirements.
1NF Drawback
Partial dependencies (EMP_NUM → EMP_NAME, JOB_CLASS_, CHG_HOUR) →→ data redundancies →→ data anomalies

13. Database Tables and Normalization
Conversion to 2NF
Step 1: Identify All Key Components
Writing each key component on a separate line, and then
writing the original key on the last line and
PROJ_NUM
EMP_NUM
PROJ_NUM, EMP_NUM
Step 2: Identify the Dependent Attributes
Writing the dependent attributes after each new key.
PROJECT ( PROJ_NUM, PROJ_NAME)
EMPLOYEE ( EMP_NUM, EMP_NAME, JOB_CLASS, CHG_HOUR)
ASSIGN ( PROJ_NUM, EMP_NUM, HOURS)

15. Database Tables and Normalization
2NF Definition
A table is in 2NF if:
It is in 1NF and
It includes no partial dependencies; that is, no attribute is dependent on only a portion of the primary key.
A table whose primary key is not composite must automatically be in 2NF. BECAUSE a partial dependency can exist only if a table has a composite primary key
It is still possible for a table in 2NF to exhibit transitive dependency; that is, one or more attributes may be functionally dependent on nonkey attributes.
2NF Drawback
Transitive dependencies (JOB_CLASS → CHG_HOUR) →→ data redundancies →→ data anomalies

16. Database Tables and Normalization
Conversion to 3NF
Create a separate table with attributes in a transitive functional dependence relationship.
Step 1: Identify Each New Determinant JOB_CLASS
Step 2: Identify the Dependent Attributes JOB_CLASS → CHG_HOUR
Step 3: Remove the Dependent Attributes from Transitive Dependencies
EMPLOYEE (EMP_NUM, EMP_NAME, JOB_CLASS)
JOB (JOB_CLASS, CHG_HOUR)
PROJECT (PROJ_NUM, PROJ_NAME)
ASSIGN (PROJ_NUM, EMP_NUM, HOURS)

18. Database Tables and Normalization
3NF Definition
A table is in 3NF if:
It is in 2NF and
It contains no transitive dependencies.

19. Improving the Design
Table structures are cleaned up to eliminate the troublesome initial partial and transitive dependencies
Normalization cannot, by itself, be relied on to make good designs
It is valuable because its use helps eliminate data redundancies

20. Improving the Design (continued)
The following changes were made:
PK assignment
Naming conventions
Attribute atomicity
Adding attributes
Adding relationships
Refining PKs
Maintaining historical accuracy
Using derived attributes

21. Improving the Design Adding relationships 3NF Project’s manager
EMP_NUM as a FK in PROJECT.
Project manager
3NF

22. Improving the Design PK assignment Naming conventions 2NF JOB_CODE
JOB_CHG_HOUR
JOB_CLASS >> JOB_DESCRIPTION
2NF

23. Improving the Design 3NF Attribute atomicity
EMP_NAME >> EMP_LNAME,EMP_FNAME,EMP_INITIAL
Adding attributes
EMP_HIREDATE
JOB_CLASS

24. 3NF Improving the Design Refining PKs
(EMP_NUM+PROJ_NUM) >> ASSIGN_NUM
Maintaining historical accuracy
ASSIGN_CHG_HOUR <<>> JOB_CHG_HOUR
Using derived attributes
ASSIGN_CHARGE = ASSIGN_HOURS × ASSIGN_CHG_HOUR
3NF

25. The Completed Database

26. The Completed Database (continued)

27. Database Tables and Normalization
Boyce-Codd Normal Form (BCNF)
A table is in Boyce-Codd normal form (BCNF) if every determinant in the table is a candidate key.
(A determinant is any attribute whose value determines other values with a row.)
If a table contains only one candidate key, the 3NF and the BCNF are equivalent.
BCNF can be violated only if the table contains more than one candidate key
BCNF is a special case of 3NF.
Figure 5.7 illustrates a table that is in 3NF but not in BCNF.
Figure 5.8 shows how the table can be decomposed to conform to the BCNF form.

28. A Table That Is In 3NF But Not In BCNF
A + B → C, D
C → B : Not transitive dependencies (A nonkey attribute is the determinant of a key attribute) → → 3NF
C : Not candidate key → → Not In BCNF
Figure 5.7

29. A + B → C, D C → B A + C → B, D C → B Figure 5.8 A + C → D C → B
The Decomposition of a Table Structure to meet BCNF Requirements
A + B → C, D
C → B
Change the PK to A+C
A + C → B, D
C → B
1NF
Figure 5.8
A + C → D
C → B

30. Sample Data for a BCNF Conversion

31. Decomposition into BCNF
Figure 5.9

32. 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
A micro view of the entities within the ER diagram
Difficult to separate normalization from E-R diagramming
Two techniques should be used concurrently

33. Normalization and Database Design
Database Design and Normalization Example: (Construction Company)
Summary of Operations:
The company manages many projects.
Each project requires the services of many employees.
An employee may be assigned to several different projects.
Some employees are not assigned to a project and perform duties not specifically related to a project.
Some employees are part of a labor pool, to be shared by all project teams.
Each employee has a (single) primary job classification. This job classification determines the hourly billing rate.
Many employees can have the same job classification.

34. Normalization and Database Design
Two Initial Entities:
PROJECT (PROJ_NUM, PROJ_NAME) [ 3NF ]
EMPLOYEE ( EMP_NUM, EMP_LNAME, EMP_FNAME, EMP_INITIAL, JOB_DESCRIPTION, JOB_CHG_HOUR)
No partial dep. Transitive dep. JOB_DESCRIPTION → JOB_CHG_HOUR [ 2NF ]

35. Normalization and Database Design
Three Entities After Transitive Dependency Removed
PROJECT (PROJ_NUM, PROJ_NAME)
EMPLOYEE ( EMP_NUM, EMP_LNAME, EMP_FNAME, EMP_INITIAL, JOB_CODE)
JOB ( JOB_CODE, JOB_DESCRIPTION, JOB_CHG_HOUR)
EMPLOYEE

36. The Modified ERD For A Contracting Company
Because the normalization process yields an additional entity (JOB),
we modify the initial ERD. M
Is held by

37. Normalization and Database Design
Creation of the Composite Entity ASSIGNMENT
ASSIGNMENT
Is held by
The Final ( Implementable) ERD for the Contracting Company

38. Normalization and Database Design
Attribute ASSIGN_HOUR is assigned to the composite entity ASSIGN.
“Manages” relationship is created between EMPLOYEE and PROJECT.
PROJECT (PROJ_NUM, PROJ_NAME, EMP_NUM)
ASSIGNMENT (ASSIGN_NUM, ASSIGN_DATE , ASSIGN_HOURS, ASSIGN_CHG_HOUR , ASSIGN_CHARGE, EMP_NUM, PROJ_NUM)
EMPLOYEE (EMP_NUM, EMP_LNAME, EMP_FNAME, EMP_INITIAL, EMP_HIREDATE, JOB_CODE)
JOB (JOB_CODE, JOB_DESCRIPTION, JOB_CHG_HOUR)
Manages

40. Higher-Level Normal Forms
In some databases, multiple multivalued attributes exist
4NF Definition
A table is in 4NF if it is in 3NF and has no multiple sets of multivalued dependencies.

41. Higher-Level Normal Forms
An employee can have multiple assignments and can also be involved in multiple service organization.
EMP_SERVICE (volunteer work) and EMP_ASSIGN (assigned project) each may have many different values.
The table contain two sets of multivalued dependencies.
Independent 1

42. A Set of Tables in 4NF
The solution is to eliminate the problems caused by independent multivalued dependencies.

44. Denormalization
Creation of normalized relations is important database design goal
Processing requirements should also be a goal
If tables decomposed to conform to normalization requirements
Number of database tables expands
Joining larger number of tables takes additional disk input/output (I/O) operations and processing logic
Reduces system speed

45. Denormalization
Normalization is only one of many database design goals.
Normalized (decomposed) tables require additional processing, ( Join : additional I/O operations ) reduce system speed.
CUSTOMER( CUS_NUM, CUS_NAME, … , ZIP_CODE, CITY)
Is it really practical? ZIP(ZIP_CODE, CITY)
Some degree of denormalization →→ increase processing speed
transitive dep.

46. Denormalization
Normalization purity is often difficult to sustain in the modern database environment.
The conflict between design efficiency, information requirements, and processing speed are often resolved through compromises that include denormalization.
In fact, we used a 2NF structure in the JOB table (Fig.5.6) to decrease the likelihood of referential integrity violations.
JOB table
Original PK: JOB_CLASS
New PK: JOB_CODE
EMPLOYEE table
Original FK: JOB_CLASS
New FK: JOB_CODE
Use denormalization cautiously.

47. The Initial 1NF Structure

48. Identifying the Possible PK Attributes

49. Table Structures Based On The Selected PKs
Foreign key