Normalization of Database Tables

Normalization of Database Tables
Database Tables and

Normalization
 Normalization is a process for assigning attributes
to entities. It reduces data redundancies and helps
eliminate the data anomalies.
 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.
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.
 The table whose contents correspond to the
reporting requirements is shown in Table 5.1.
Scenario
A few employees works Project Num :

for one project. 15
Project Name :
Evergreen
Employee Num :
101, 102, 103,
105
Sample Form
Project Num :
15
Project Name : Evergreen
Emp Emp Job Class Chr Hrs Total

Num
101 Name Hours Billed
102
103
105
Table Structure Matches
the Report Format
Database Tables and
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.
 Addition anomalies.
 Deletion anomalies.
Database Tables and
Normalization
 Conversion to First Normal Form

– A relational table must not contain repeating
groups.
– Repeating groups can be eliminated by adding
the appropriate entry in at least the primary key
column(s).
Data Organization: First Normal Form
After
Before
First Normal Form (1 NF)
 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.
 All attributes are dependent on the primary
key.
Dependency Diagram
 Dependency Diagram
– The primary key components are bold, underlined, and
shaded in a different color.
– The arrows above entities indicate all desirable
dependencies, i.e., dependencies that are based on PK.
– The arrows below the dependency diagram indicate less
desirable dependencies -- partial dependencies and
transitive dependencies.
Second Normal Form (2 NF)
 Conversion to Second Normal Form

– Starting with the 1NF format, the database can be
converted into the 2NF format by
 Writing each key component on a separate line,
and then writing the original key on the last line
and
 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)
Dependency Diagram
Second Normal Form (2 NF)
A table is in 2NF if:

 It is in 1NF and
 Itincludes no partial dependencies; that is,
no attribute is dependent on only a portion
of the 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.)
Third Normal Form (3 NF)
 Conversion to Third Normal Form

– Create a separate table with attributes in a
transitive functional dependence relationship.

EMPLOYEE (EMP_NUM, EMP_NAME, JOB_CLASS)
JOB (JOB_CLASS, CHG_HOUR)
Third Normal Form (3 NF)
 3NF Definition
– A table is in 3NF if:
 It is in 2NF and
 It contains no transitive dependencies.
The
Completed
Database
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 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.
A Table That Is In 3NF
But Not In BCNF
The Decomposition of a Table Structure
to Meet BCNF Requirements
Sample Data for a BCNF Conversion
Decomposition into BCNF
BCNF Definition
 BCNF Definition
– A table is in BCNF if every determinant in that
table is a candidate key. If a table contains
only one candidate key, 3NF and BCNF are
equivalent.
Normalization
– Normalization will help us identify correct

and appropriate TABLES.
– Until Now we have 4 tables

NEXT ........
– We are going to identify the relationships

between entities (tables) including their
cardinality, connectivity.
– We have to list out the Business Rules.

Business Rules
 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.
Normalization and Database
Design
 Two Initial Entities:

EMPLOYEE (EMP_NUM, EMP_LNAME, EMP_FNAME,
EMP_INITIAL, JOB_DESCRIPTION, JOB_CHG_HOUR)
Design
ThreeEntities After Transitive Dependency

Removed

EMPLOYEE (EMP_NUM, EMP_LNAME, EMP_FNAME, EMP_INITIAL,
JOB_CODE)
JOB (JOB_CODE, JOB_DESCRIPTION, JOB_CHG_HOUR)
The Modified ERD
Creation of Composite Entity ASSIGN
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)

EMPLOYEE (EMP_NUM, EMP_LNAME, EMP_FNAME,
EMP_INITIAL,
EMP_HIREDATE, JOB_CODE)
JOB (JOB_CODE, JOB_DESCRIPTION, JOB_CHG_HOUR)
ASSIGN (ASSIGN_NUM, ASSIGN_DATE, PROJ_NUM,
EMP_NUM,
ASSIGN_HOURS)
Relational Schema
Higher-Level Normal Forms
 4NF Definition
– A table is in 4NF if it is in 3NF and has no
multiple sets of multivalued dependencies.
A Set of Tables in 4NF
Denormalization
 Normalization is only one of many database

design goals.
 Normalized (decomposed) tables require
additional processing, reducing system speed.
 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.
SUMMAR
Y
The Initial 1NF Structure
Identifying the Possible PK Attributes
Table Structures Based On
The Selected PKs

Normalization of Database Tables

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Normalization of Database Tables

Database Tables and

 The highest level of normalization is not always

 The Need for Normalization

A few employees works Project Num :

Emp Emp Job Class Chr Hrs Total

 Problems with the Figure 5.1

 Conversion to First Normal Form

 Conversion to Second Normal Form

PROJECT (PROJ_NUM, PROJ_NAME)

A table is in 2NF if:

 Conversion to Third Normal Form

PROJECT (PROJ_NUM, PROJ_NAME)

– Normalization will help us identify correct

PROJECT (PROJ_NUM, PROJ_NAME)

– We are going to identify the relationships

PROJECT (PROJ_NUM, PROJ_NAME)

 The company manages many projects.

 Two Initial Entities:

ThreeEntities After Transitive Dependency

PROJECT (PROJ_NUM, PROJ_NAME)

 Attribute ASSIGN_HOUR is assigned to the composite

PROJECT (PROJ_NUM, PROJ_NAME, EMP_NUM)

 Normalization is only one of many database

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