Normalization works through a series of stages called normal forms

Lecture7_ch07.ppt
Database Principles: Fundamentals of Design, Implementations and Management

CHAPTER 7 Normalizing Database Designs

*

Objectives

In this chapter, you will learn:
What normalization is and what role it plays in the database design process
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 ER modeling are used concurrently to produce a good database design
That some situations require denormalization to generate information efficiently
*

Database Tables and Normalization

Normalization
Process for evaluating and correcting table structures to minimize data redundancies
Reduces data anomalies
Works through a series of stages called normal forms:
First normal form (1NF)
Second normal form (2NF)
Third normal form (3NF)
*

Database Tables and Normalization (cont..)

Normalization (cont..)
2NF is better than 1NF; 3NF is better than 2NF
For most business database design purposes, 3NF is as high as needed in normalization
Highest level of normalization is not always most desirable
Denormalization produces a lower normal form
Price paid for increased performance is greater data redundancy
*

The Need for Normalization

Example: company that manages building projects
Charges its clients by billing hours spent on each contract
Hourly billing rate is dependent on employee’s position
Periodically, report is generated that contains information such as displayed in Table 5.1
The Need for Normalization

*

The Need for Normalization

*

*

The Need for Normalization (cont..)

Structure of data set in Figure 7.1 does not handle data very well
Table structure appears to work; report generated with ease
Unfortunately report may yield different results depending on what data anomaly has occurred
Relational database environment suited to help designer avoid data integrity problems
*

The Normalization Process

Each table represents a single subject
No data item will be unnecessarily stored in more than one table
All attributes in a table are dependent on the primary key
Each table void of insertion, update, deletion anomalies
Void = depourvu de

*

The Normalization Process (cont..)

*

*

The Normalization Process (cont..)

Objective of normalization is to ensure all tables in at least 3NF
Higher forms not likely to be encountered in business environment
Normalization works one relation at a time
Progressively breaks table into new set of relations based on identified dependencies
*

Conversion to First Normal Form

Repeating group
Derives its name from the fact that a group of multiple entries of same type can exist for any single key attribute occurrence
Relational table must not contain repeating groups
Normalizing table structure will reduce data redundancies
Normalization is three-step procedure
*

Conversion to First Normal Form (cont.)

Step 1: Eliminate the Repeating Groups
Present data in tabular format, where each cell has single value and there are no repeating groups
Eliminate nulls: each repeating group attribute contains an appropriate data value
Step 2: Identify the Primary Key
Primary key must uniquely identify attribute value
New key must be composed
Conversion to First Normal Form (cont..)

*

Conversion to First Normal Form (cont..)

*

Conversion to First Normal Form (cont..)

Step 3: Identify All Dependencies
Dependencies can be depicted with help of a diagram
Dependency diagram:
Depicts all dependencies found within given table structure
Helpful in getting bird’s-eye view of all relationships among table’s attributes
Makes it less likely that will overlook an important dependency
*

Conversion to First Normal Form (cont..)

*

*

Conversion to First Normal Form (cont.)

First normal form describes tabular format in which:
All key attributes are defined
There are no repeating groups in the table
All attributes are dependent on primary key
All relational tables satisfy 1NF requirements
Some tables contain partial dependencies
Dependencies based on part of the primary key
Sometimes used for performance reasons, but should be used with caution
Still subject to data redundancies
Conversion to Second Normal Form

Relational database design can be improved by converting the database into second normal form (2NF)
Two steps
*

*

Conversion to Second Normal Form (cont..)

Step 1: Write Each Key Component
on a Separate Line
Write each key component on separate line, then write original (composite) key on last line
Each component will become key in new table
Step 2: Assign Corresponding Dependent Attributes
Determine those attributes that are dependent on other attributes
At this point, most anomalies have been eliminated
Conversion to Second Normal Form (cont..)

*

*

Conversion to Second Normal Form (cont..)

Table is in second normal form (2NF) when:
It is in 1NF and
It includes no partial dependencies:
No attribute is dependent on only portion of primary key