Normalization_is_the_process_of_efficiently_organizing_data_in_a_database

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DATABASE & DATABASE DESIGN

What is Normalization?

Normalization is the process of efficiently organizing data

in a database. There are two goals of the normalization

process: eliminating redundant data and ensuring that the

database design does not suffer from any Update, delete

and insert anomalies . Both of these are worthy goals as

they reduce the amount of space a database consumes

and ensure that data is logically stored

Example of Anomalies:

Consider the following database design:

Student

Enroll No Name Section Mailing

Address

Club

Membership06BS1256 Shipra A CC-89,Xmas

Street,

Gurgaon

Finance

06BS1909 Krishna K A-

4555,Christ

Rd,Chennai

IT

06BS1256 Shipra A CC-89,Xmas Marketing


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Street,

Gurgaon06BS1909 Krishna K A-

4555,ChristRd,Chennai

HR

06BS1890

Gokul J ABC,Saket,N

Delhi

Finance

In the table student the primary key is Enroll No and

Club Membership. It is seen from the table that a student

will be opting for a number of club memberships and as is

evident from the table that in case of a student opting for

no of club memberships there is repetition of students

details like name,section ,mailing address(see row 1 and3).It results not only in redundancy of data but can also

result in data inconsistency since any changes which have

to be made have to be made at multiple places.If Shipras

section changes from Section A to Section C changes will

will have to be made in both rows 1 and 3.If row 3 is not

updated it will result in data inconsistency and henceresult in Update Anomaly.

Insert Anomaly:

Consider a case of a new student joining IBS gurgaon in

Section D but he doesnt have any club memberships


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.Since Club Memebership is a primary key and Primary

key cannot be left blank or have NULL Value we cannot

insert the details of the new student till he becomes a

member of atleast one club.This is refereed to as Insert

Anomaly.

Delete Anomaly:

Consider a case where Gokul (Row 5 of the table) is no

longer a member of Finance Club. We will have to delete

Gokuls record since Club Membership cannot be NULL or

blank since its a primary key.If we delete Gokuls record

we loose all information about gokuls section ,mailing

address etc.This is a Delete Anomaly.

To prevent instances like these the database community

has developed a series of guidelines for ensuring that

databases are normalized. These are referred to as normal

forms and are numbered from one (the lowest form of

normalization, referred to as first normal form or 1NF)

through five (fifth normal form or 5NF). In practicalapplications, you'll often see 1NF, 2NF, and 3NF along

with the occasional 4NF. Fifth normal form is very rarely

seen.

It's important to point out that they are guidelines and

guidelines only . Occasionally, it becomes necessary to


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stray from them to meet practical business requirements.

However, when variations take place, it's extremely

important to evaluate any possible ramifications they

could have on the system and account for possible

inconsistencies.

First Normal Form (1NF)

First normal form (1NF) sets the very basic rules for an

organized database: Remove all multivalued attributes. No comma

separated values are allowed in a single field of the

database.

For example

Customer


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Customer ID

FirstName Surname

TelephoneNumber

123 Robert Ingram 555-861-2025

456 Jane Wright

555-403-1659,555-776-4100

789 Maria Fernandez 555-808-9633

This table is not in 1 NF since Telephone Number contains

Multiple Attributes in one cell/field.

Remedies:

Customer ID

FirstName Surname

Tel. No.1

Tel. No.2

Tel.No. 3

123 Robert Ingram 555-861-2025

456 Jane Wright 555-403-1659555-776-4100


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789 Maria Fernandez 555-808-9633

Have different Number of Columns for the

repeating field Telephone No. But this remedy also

comes with its problems since the max no of

telephone numbers for a customer would be difficult

to ascertain .Like in this table we see that most of

the fields for Tel No 2 and Tel No 3 are blank.This

contributes to redundancy .

Have Separate rows for different Telephone

nos. This also contributes to redundancy since for

every row except for Telephone No all other

attributes will get repeated.

Best remedy would be to divide this table into

two .The problem of both redundancy and

Multivalued Attributes gets solved.

Customer

Customer ID

FirstName Surname

Customer TelephoneNumber

Customer ID

TelephoneNumber


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123 Robert Ingram

456 Jane Wright

789 Maria Fernandez

123 555-861-2025

456 555-403-1659

456 555-776-4100

789 555-808-9633

SECOND NORMAL FORM (2NF)

Second normal form (2NF) further addresses the concept

of removing duplicative data:

Applicable to tables which have a composite

primary key.

2 NF states that all Non Key Attributes shouldbe fully functionally dependent on the key

attributes.

2 NF states that all Non key Attributes (Section, Mailing

Address, Name) in table student should be fully

functionally dependent on the Key attributes(Enroll No,


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Club Membership).That means no Non Key attribute

should get its value only from a part of the primary key.

In the table student all three Non key Attributes are

dependent on Enroll No and not Club Membership. For the

table to be in 2NF them all must derive their values from

the combination of both Enroll No and Club Membership.

To get this table in 2NF we divide the table further by

taking out the non key attribute which has a partial

functional dependency on part of primary key.For exampleName(Non key attribute) and Enroll No (part of the

Primary key Attribute) will be palced in another table.

Third Normal Form (3NF)

Third normal form (3NF) goes one large step further:

Meet all the requirements of the second normal

form.

Remove columns that are not dependent upon

the primary key directly .There should be no

transitive dependency .

For egs:

Employee

Employee ID Dept Id Dept Name


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In This table Employee Id is the Primary key

.Employee ID determines the Dept ID (the dept for

which the employee is working) and Dept ID

determines the Dept Name. Thus in this table there

is transitive dependency because Employee ID

determines Dept ID and Dept ID determines Dept

Name .3NF states that all non key attributes should

be directly dependent on the primary key.

To get this table in 3 NF we remove Dept Name andDept ID and put it another table.

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Normalization_is_the_process_of_efficiently_organizing_data_in_a_database