2. INTRODUCTION
One of the most important steps in designing a database is
ensuring that the data is properly distributed among its tables.
With proper data structures, illogically or inconsistently stored
data can cause a number of problems. In a relational database, a
logical and efficient design is just as critical. A poorly designed
database may provide erroneous information, may be difficult to
use, or may even fail to work properly. A poorly design database
can cripple an application, producing problems with redundancy,
in accuracy, consistency and concurrency of data. Normalization
is a process that serves to reduce, if not eliminate, these
problems with data.
3. DESCRIPTION OF NORMALIZATION
Normalization is the process of organizing data to
minimize redundancy. The goal of database
normalization is to decompose relations with
anomalies in order to produce smaller, well-
structured relations. Normalization usually
involves dividing large tables into smaller (and
less redundant) tables and defining relationships
between them. The objective is to isolate data so
that additions, deletions, and modifications of a
field can be made in just one table and then
propagated through the rest of the database via
the defined relationships.
4. Normalization Levels
There are a few rules for database normalization. Each
rule is called a "normal form." If the first rule is observed,
the database is said to be in "first normal form." If the first
three rules are observed, the database is considered to
be in "third normal form." Although other levels of
normalization are possible, third normal form is
considered the highest level necessary for most
applications. There is a number of normalization levels
from 1. normal form through 5. normal form. Each normal
form describes how to get rid of some specific problem,
usually related to redundancy. Below are description with
examples of level one to three normal forms.
5. First Normal Form
Eliminate repeating groups in individual
tables.
Create a separate table for each set of
related data.
Identify each set of related data with a
primary key.
6. Second Normal Form
Create separate tables for sets of values
that apply to multiple records.
Relate these tables with a foreign key.
Records should not depend on anything
other than a table's primary key (a
compound key, if necessary).
7. Third Normal Form
Eliminate fields that do not depend on the
key. Third normal form prohibits
transitive dependencies. A transitive
dependency exist when any attribute in a
table is dependent of any other non-key
attribute in that table.
8. Other Normalization Forms
Fourth normal form, also called Boyce Codd
Normal Form (BCNF), and fifth normal form
do exist, but are rarely considered in practical
design. Disregarding these rules may result in
less than perfect database design, but should
not affect functionality.
9. Examples Of Normalization
Table
1. Unnormalized table:
Student advisor Adv- Class 1 Class 2 Class 3
room
1022 Jones 412 101-07 143-01 159-02
4123 Smith 216 201-01 211-02 214-01
10. First Normal Form: No Repeating
Groups
Studet Advisor Adv-room class
1022 jones 412 101-07
1022 jones 412 143-01
1022 jones 412 159-02
4123 smith 216 201-01
4123 Smith 216 211-02
4123 smith 216 214-01
11. Second Normal Form: Eliminate Redundant Data
registration
student
student class
Student Advisor Adv-
room
1022 101-07
1022 Jone 412
1022 143-01
s
4123 Smitt 216 1022 159-01
4123 201-01
4123 211-02
4123 214-01
12. Third Normal Form: Eliminate Data Not Dependent On
Key
faculty
student
Student advisor Name Room Depart
1022 Jones
Jones 412 42
4123 smith
Smith 216 42
13. Normalising A Database Should Be Able To
Achieve The Following Four Goals:
Arranging data into logical groups such that
each group describes a small part of the whole
Minimizing the amount of duplicated
data stored in a database
Building a database in which you can access
and manipulate the data quickly and
efficiently without compromising the integrity of
the data storage
Organising the data such that, when you
modify it, you make the changes in only one
place
14. By Normalization The Following Problem In
Relational Database Are Solve
Use storage space efficiently
Eliminate redundant data
Reduce or eliminate inconsistent data
Ease the database maintenance burden
Enforce referential integrity.
Data integrity
Minimize modification anomalies
17. Un Normalized Database
Problem
Repetition of information
Inability to represent certain information
Loss of information
Difficulty to maintain information
18. SQL PROGRAM
Create table user
(user_id Int (8),
first_name Char (15),
last_name Char (15),
sex char (7),
home town Char (16),
relationship_status (8),
interested_in Char (7),
religious _views char (15),
political_view Char (15));
Create table user affiliation
(user_id Int (8),
Affiliation_id int (4),
Foreign key (user_id, Affiliation_id));
19. CONT. OF SQL PROG.
Create table Affiliation
(Affiliation_id int (4),
Description char (15),
Member_count int (10));
Create table user_phone_numbers
(user_id Int (8),
Phone_number int (15),
Phone_type char (10)
user_id));
Create table user_screen_name
(user_id Int (8),
Screen_name varchar (30),
Im_service char (10),
Foreign key ((user_id Int ));
20. CONT. OF SQL
Create table user_work_history
(user_id Int (8),
Company_affiliation_id int (4),
Company_name char (20),
Job_title char (20)
Foreign key (Company_affiliation_id,
user_id));
21. PROBLEM TO FACE IF DATABASE DESIGN IS
NOT NORMALIZED
Normalisation is part of successful database design.
Without normalisation, there will be Problem of high data
redundancy – if data in the database can be found in two
different locations (direct redundancy) or if data can be
calculated from other data items (indirect redundancy)
then the data is said to contain redundancy. Data should
only be stored once and avoid storing data that can be
calculated from other data already held in the database.
Not normalizing database systems can be inaccurate,
slow, and inefficient and they might not produce the data
one may expect. It is adviceable to always use the
normalization process to design efficient and functional
databases. By normalizing, data will be store where it
logically and uniquely belongs.
22. DISADVANTAGE OF NORMALIZATION
The only real drawback to having a highly normalization database structure is that one may need a
large number of joins to pull back the records the application needs to function.
For example in the social network site schema above one will requires a whopping six joins to
retrieve a single user's information.
select * from Users u
inner join UserPhoneNumbers upn
on u.user_id = upn.user_id the fact here is that one
inner join UserScreenNames usn need six joins -- or six
on u.user_id = usn.user_id individual queries, to
inner join UserAffiliations ua retrieve a single user
on u.user_id = ua.user_id information. This is time
inner join Affiliations a consuming and slow
on a.affiliation_id = ua.affiliation_id dawn your system
inner join UserWorkHistory uwh performance
on u.user_id = uwh.user_id
inner join Affiliations wa
on uwh.affiliation_id = wa.affiliation_id
23. CONCLUTION
There are advantages and disadvantages to normalizing database schemas but
the big question now is when is it appropriate to normalize and when not
to. It is true that Database normalization is a formal process of designing one
database to eliminate redundant data, utilize space efficiently and reduce
update errors. Anyone who has ever taken a database class has it drummed
into their heads that a normalized database is the only way to go. This is true for
the most part. However there are certain scenarios where the benefits of
database normalization are outweighed by its costs. So I think people should not
normalize for the sake of normalization or because one school professor told
them to but because the data tells them to for the following reasons.
Normalization makes sense to their team, Normalization provides better
performance. (they’re automatically measuring all the queries that flow through
their software, right?) Normalization prevents an onerous amount of duplication
or avoids risk of synchronization problems that their problem domain or users
are particularly sensitive to and finally that Normalization allows them to write
simpler queries and code.
25. REFERENCES
[1] R. Ramakrishnan, J. Gehrke “Database Management System”, McGraw-Hill,
New York 2003
[2] Dare O. “When Not To Normalize Your SQL Database”
http://www.25hoursaday.com/weblog/commentview.aspx?
[3] Microsoft Support, “Description Of The Database Normalization Basics”
http://support.microsoft.com/kb/283878#top
