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ITDB 1102Introduction to Database

Normalization 1

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Normalization

•

Normalization is a database design Technique.• The purpose of normalization is to remove redundancy

(duplication).

• One Piece of information is stored in one place in the

database.

2

Normalization is the process of decomposing

relation with anomalies into small relations while

ensuring data integrity and eliminating dataredundancy

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Data integrity

•Data integrity: all of the data in the database is consistent,and satisfies all integrity constraints.

3

Dept_IDDOBStd_NameStd _ID

D0013/10/1994AhmadS121

D00223/6/1993SalmaS122

D0012/9/1994KhalidS123

Dept_NameDept_ID

ITD001

EnggD002

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Data Redundancy

• Data is said to contain redundancy if:

• Direct redundancy: Data in the database can be found intwo different locations

• Indirect redundancy :Data can be calculated from other

data items).

• Data should only be stored once and avoid storing data that can be

calculated from other data already held in the database.

4

Dept_NameDept_IDDOBStd_NameStd _ID

Dept_NameDept_ID

AgePhone_NoDOBStd_NameStd _ID

19927363483/10/1994AhmadS121

209863762123/6/1993KhalidS122

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Data Redundancy

• If redundancy exists in the database then problems can

arise when the database is in normal operation:

• Insert : When data is inserted the data must be

duplicated correctly in all places where there is

redundancy.

• Update: When data is modified in the database, if the

data being changed has redundancy, then all versions of

the redundant data must be updated simultaneously.

• The removal of redundancy helps to prevent insertion,

deletion, and update errors, since the data is only available

in one attribute of one table in the database. 5

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Normal Forms

• The data in the database can be considered to be in one

of a number of `normal forms'.

• Normal form of the data indicates how much

redundancy is in that data. The normal forms have a

strict ordering

• 1st Normal Form

• 2nd Normal Form

• 3rd Normal Form

• To be in a particular form requires that the data meets the criteria to also be

in all normal forms before that form. Thus to be in 2nd normal form the data

must meet the criteria for both 2nd normal form and 1st normal form. The

higher the form the more redundancy has been eliminated. 6

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Anomalies

7

EmpId Ename DeptName Salary Course_Title Date_Completed

100 Ali Marketting 4800 SPSS 6/19/2011

100 Ali Marketting 4800 Surveys 10/7/2011

140 Said Accounting 5200 Tax Acc 12/8/2011

110 ahmed Infosystem 4300 Visual Basic 1/12/2011

110 ahmed Infosystem 4300 C++ 4/22/2011

150 Khalid Marketting 4200 SPSS 6/19/2011

150 khalid Marketting 4200 Java 8/12/2011

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1. Insert AnomalyInsert Anomaly – The insert anomaly refers to a situation where in

you cannot insert data into the database because of an artificial

dependency among columns in a table.

• A record about an entity cannot be inserted into the table

without first inserting information about another entity.

• Example:• The primary key for this table is the combination of Emp_ID and

Course_Title.

• Therefore, to insert a new row, the user must supply values for both

Emp_ID and Course_Title (because primary key values cannot be null

or nonexistent).

• This is an anomaly. Because the user should be able to enter

employee data without supplying course data.8

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2. Delete AnomalyDelete Anomaly– It refers to a situation where in the deletion of

data causes unintended loss of other data.

• A record cannot be deleted without deleting a record about a

related entity.

• Cannot delete a sales order without deleting all of the

customer’s information.

• Example:

• Suppose that the data for employee number 140 are deleted from

the table.

•

This will result in losing the information that this employeecompleted a course (Tax Acc) on 12/8/200X.

• In fact it results in losing the information that this course had an

offering that completed on that date.9

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3. Update Anomaly

Update Anomaly – An update anomaly refers to a situationwhere in an update of a single data value requires multiple

rows to be updated.

Cannot update information without changing information in

many places.

To update customer information, it must be updated for each

sales order the customer has placed.

• Example:

• Suppose that employee number 100 gets a salary increase.

• We must record the increase in each of the rows for thatemployee (two occurrences in above table); otherwise the data

will be inconsistent.

10

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Normalization

What is Normalization? • Normalization is the process of decomposing relations with

anomalies to produce smaller relations with minimal

redundancy.

The goal of normalization:

1. Minimize data redundancy, thereby avoiding anomalies

and conserving storage space.

2. Simplify the enforcement of referential integrity

constraints.

3. Make it easier to maintain data (insert, update, and

delete).11

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Normalization

Advantages:

1. Reduce data redundancy (duplication of data).

2. Eliminate data inconsistency (improper data)

3. Reduce the amount of space a database

consumes.

4. Reduces time to search a data.

5. Reduces time to sort data. 12

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Functional Dependencies

• Functional dependency describes the relationship between

attributes in a relation.

• If A and B are attributes of a relation R, B is functionally

dependent on A (den. A → B), if each value of A in R is associated

with exactly one value of B in R.

• Example:

13

Tutor_NameTutor_NoSur_nameFirst_NameMatric_No

Tutor_No -> Tutor_Name Determinant Dependent

employee

A BB is functionally dependent on A

Determinant: Attribute or set of attributes

on the left hand side of the arrow

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Functional Dependencies• Identify the candidate key for a relation:

• Recognize the attribute (group of attributes) that uniquelyidentifies each row in a relation.

• All of the attributes that are not part of the primary key (non-

primary key attributes) should be functionally dependent on the

key.

14

Staff-NO PositionPosition is functionally

dependent on Staff-NO1:1

10002 HOD

Position Staff NOStaff NO is functionally

dependent on Position1:M

10002

HOD

10002

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The Normal Form

1. First Normal Form ( 1NF )

2. Second Normal Form ( 2NF )

3. Third Normal Form ( 3NF )

4. Fourth Normal Form ( 4NF )

5. Boyce-Codd Normal Form ( BCNF )

15

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Process of Normalization:•

Un normalized form (UNF): A table that contains one or morerepeating groups.

• Repeating group: An attribute or group of attributes within a

table that occurs with multiple values for a single occurrence

of the nominated key attributes of that table.

16

Std ID Name Date

of

Birth

AdvisorID Advisor

Name

Advisor

Phone

No

CourseID Course

Name

Credit Hrs Passing

grade

Std

Mark

S01234 Ali 5/7/90 11 Mr. Aijaz 123 ITSE1100

ITNT1103

ITDB1102

Multimedia

Hardware

Database

6

5

5

D

C

C

60

70

50

S01235 Said 6/5/89 12 Ms.Aysha 124 ITSE1100

ITNT1103

Multimedia

Hardware

6

5

D

C

70

80

Repeating group

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First Normal Form•

A relation in which the intersection of each rowand column contains one and only one value.

• UNF → 1NF:

1. Remove repeating groups- by entering

appropriate data in the empty columns of

rows.

2. Placing repeating data along with a copy of the

original key attribute in a separate relation.3. Identifying a primary key for each of the new

relations.17

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Second normal form (2NF):A relation is said to be in 2NF if is in 1NF and no partial functional

dependency.• Partial functional dependency: A functional dependency in which

one or more non key attributes are functionally dependent on part

(but not full/all) of the primary key.

• Note: Applies to relations with composite keys (primary key

composed of two or more attributes).

• A relation with a single attribute primary key is in 2NF.

• 1NF → 2NF:

1. Remove partial dependencies

2. The functionally dependent attributes are removed from the

relation by placing them in a new relation along with a copy of

their determinant. (Part of the primary key)18

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Third normal form (3NF):A relation is said to be in 3NF if it is in 2NF and no transitively

dependency exist.

• Transitive dependency: A relationship between two (or more)

non-key attributes.

• When one non-key attribute is functionally dependent onanother non-key attribute

• 2NF → 3NF:

• The transitively dependent attributes are removed from therelation by placing them in a new relation along with a copy of

their determinant.19

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An example for Normalization• Consider the following table which is not in the first normal form:

20

Std ID Nam

e

Date

of

Birth

Advisor-

ID

Advisor

Name

Advisor

Phone

No

CourseID Course

Name

Credit

Hrs

Passing

grade

Std

Mark

S01234 Ali 5/7/9

0

11 Mr. Aijaz 123 ITSE1100

ITNT1103

ITDB1102

Multimedia

Hardware

Database

6

5

5

D

C

C

60

70

50

S01235 Said 6/5/8

9

12 Ms.Aysha 124 ITSE1100

ITNT1103

Multimedia

Hardware

6

5

D

C

70

80

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To bring the table to 1NF:

1. Adjust the table to have one value in each cell.

2. Separate the repeating group fields into a separate table.

• The repeating fields are Student ID, Name, Date of Birth, Advisor

ID, Advisor Name and Advisor Phone No.

3. Provide a link (by foreign key) between student table and

Student-course table.

4. Determine the primary keys and foreign keys in each table21

Student

ID

Name Date of

Birth

AdvisorID Advisor

Name

Advisor

Phone

CourseID Course

Name

Credit

Hrs

Passing

Grade

Std

Mark

S01234 Ali 5/7/90 11 Mr. Aijaz 123 ITSE1100 Multimedia 6 D 60

S01234 Ali 5/7/90 11 Mr. Aijaz 123 ITNT1103 Hardware 5 C 70

S01234 Ali 5/7/90 11 Mr. Aijaz 123 ITDB1102 Database 5 C 50

S01235 Said 6/5/89 12 Ms. Aysha 124 ITSE1100 Multimedia 6 D 70

S01235 Said 6/5/89 12 Ms. Aysha 124 ITNT1103 Hardware 5 C 80

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First Normal Form

• Student Table

• Primary Key – StudentID

22

StudentID Name Date of

Birth

AdvisorID Advisor Name Advisor

Phone No

S01234 Ali 5/7/90 11 Mr. Aijaz 123

S01235 Said 6/5/89 12 Ms. Aysha 124

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• Student- Course Table

1. The StudentID is not unique itself, as one student may take

multiple courses.

2. The Course_ID is not unique itself, as many students may takethe same course, then StudentID + CourseID is unique, so the

primary key is StudentID + CourseID.

• Primary Key: StudentID + CourseID (Composite key)

• Foreign Key: StudentID, it links Student Course Table with Student

Table.

23

StudentID CourseID Course Name Credit Hrs Passing Grade Std Mark

S01234 ITSE1100 Multimedia 6 D 60

S01234 ITNT1103 Hardware 5 C 70

S01234 ITDB1102 Database 5 C 50

S01235 ITSE1100 Multimedia 6 D 70

S01235 ITNT1103 Hardware 5 C 80

FK

PK (Composite key)

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0 NF 1NF 2NF 3NF

Std ID Student

Name Std ID PK

Date of Birth Name

Advisor-ID Date of Birth

Advisor Name Advisor-ID

Advisor

Phone No

Advisor Name

CourseID Advisor Phone No

Course Name Student-course

Credit Hrs Std ID FK

Passing grade CourseID

Std Mark Course Name

Credit Hrs

Passing grade

Std Mark

Primary Key Foreign Key

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Second Normal Form (2NF)• 2NF applies on Student- Course table only because it contains a

composite key. To bring this table to 2NF:1. Find out the non key fields which do not depend on the whole

primary key and place them in a separate table with a link (Foreign

Key).

For the Student - Course table the primary key is: StudentID + CourseID

2. The Non-key fields Course Name, Credit Hours, and Passing Grade

depend on the CourseID only which is a portion of the primary key.

3. The remaining field is StdMark which depends on the StudentID +CourseID which is the primary key where it gives the mark of a

student in a specific course.

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Second Normal Form (2NF)

• Student Table

• Primary Key – StudentID

26

StudentID Name Date of

Birth

AdvisorID Advisor Name Advisor

Phone No

S01234 Ali 5/7/90 11 Mr. Aijaz 123

S01235 Said 6/5/89 12 Ms. Aysha 124

Student table is already in 2NF because it has a primary key formed

with one attribute (StudentID).

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Second Normal Form (2NF)Divide the Student-Course

table into two tables:1. Student-Course table

2. Course table.

Student-Course table

• Primary Key:

StudentID+CourseID

• Foreign Key:

StudentID, CourseID

27

StudentID CourseID Std Mark

S01234 ITSE1100 60

S01234 ITNT1103 70

S01234 ITDB1102 50

S01234 ITDB1102 70

S01235 ITSE1100 70

S01235 ITNT1103 80

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Second Normal Form (2NF)• Course Table

• Primary Key: CourseID

28

CourseID Course Name Credit Hours Passing grade

ITSE1100 Multimedia 6 D

ITNT1103 Hardware 5 C

ITDB1102 Database 5 C

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0 NF 1NF 2NF 3NF

Std ID Student Student

Name Std ID PK Std ID PK

Date of Birth Name Name

Advisor-ID Date of Birth Date of Birth

Advisor Name Advisor-ID Advisor-ID

Advisor Phone No Advisor Name Advisor Name

CourseID Advisor Phone No Advisor Phone No

Course Name Student-course Student-course

Credit Hrs Std ID FK Std ID FK

Passing grade CourseID CourseID FK

Std Mark Course Name Std Mark

Credit Hrs Course

Passing grade CourseID PK

Std Mark Course Name

Credit Hrs

Passing grade

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Third normal form (3NF)

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

• For each non key attribute (or set of attributes) that is a

determinant in a relation, create a new relation.

• That attribute (or set of attributes) becomes the primary key of

the new relation.

•

Move all of the attributes that are functionally dependent on theattribute from the old to the new relation.

• Leave the attribute (which serves as a primary key in the new

relation) in the old

• relation to serve as a foreign key that allows you to

associate the two relations.

30

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Third normal form (3NF)• Course table and Student- Course table remains the same

because they are already upto 3rd NF.

(No non-key attribute determines the other non-key attribute)

• In the Student table, a non key attribute Advisor Phone is

determined by another non key attribute Advisor Name.

• So the advisor information should be placed in a separate

table and link/association (Foreign key) with the Student table.31

non-key attribute ---> non-key attribute

Advisor Name ---> Advisor Phone

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Third normal form (3NF)• Student Table

Primary Key: StudentID Foreign Key: AdvisorID

• Advisor Table

Primary Key: AdvisorID

32

StudentID Name Date of Birth AdvisorID

S01234 Ali 5/7/90 11

S01235 Said 6/5/89 12

AdvisorID Advisor Name Advisor Phone No

11 Mr. Aijaz 123

12 Ms.Aysha 124

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0 NF 1NF 2NF 3NF

Std ID Student Student Student

Name Std ID PK Std ID PK Std ID PK

Date of Birth Name Name Name

Advisor-ID Date of Birth Date of Birth Date of Birth

Advisor Name Advisor-ID Advisor-ID Advisor-ID FK

Advisor Phone No Advisor Name Advisor Name Advisor

CourseID Advisor Phone No Advisor Phone No Advisor-ID PK

Course Name Student-course Student-course Advisor Name

Credit Hrs Std ID FK Std ID FK Advisor Phone No

Passing grade CourseID CourseID FK Student-course

Std Mark Course Name Std Mark Std ID FK

Credit Hrs Course CourseID FK

Passing grade CourseID PK Std Mark

Std Mark Course Name Course

Credit Hrs CourseID PK

Passing grade Course Name

Credit Hrs

Passing grade

PK

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Case Study:

34

UNF

Invoice_No

Invoice_date

Customer_No

Customer_Name

Customer_Address

Tax_total

Gross_Total

Net_Total

Item_code

Item_Description

Price

Quantity

Tax_percent

Tax_amount

Net_amount

Primary Key

Foreign Key

Repeating Groups: Note that each invoice has

many items, so the attributes related to the

item in the invoice are repeated.

UNF 1NF

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35

UNF 1NF

Invoice_No Invoice

Invoice_date Invoice_No

Customer_No Customer_No

Customer_Name Invoice_dateCustomer_Address Customer_Name

Tax_total Customer_Address

Gross_Total Tax_total

Net_Total Gross_Total

Item_code Net_Total

Item_Description Item

Price Invoice_No

Quantity Item_code

Tax_percent Item_DescriptionTax_amount Price

Net_amount Quantity

Tax_percent

Tax_amount

Net_amount

Primary Key

Foreign Key

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0 NF 1NF 2NF 3NF

Matric_No Student Student

Name Matric_No Matric_No

Date_Of_Birth Name Name

Subject Date_Of_Birth Date_Of_Birth

Grade

Record Record

Matric_No Matric_No

Subject Subject

Grade Grade

Primary Key

Foreign Key

UNF 1NF 2NF

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UNF 1NF

Invoice_No Invoice

Invoice_date Invoice_No

Customer_No Customer_No

Customer_Name Invoice_date

Customer_Address Customer_Name

Tax_total Customer_Address

Gross_Total Tax_total

Net_Total Gross_Total

Item_code Net_Total

Item_Description Item

Price Invoice_No

Quantity Item_code

Tax_percent Item_Description

Tax_amount Price

Net_amount Quantity

Tax_percent

Tax_amount

Net_amount

Primary Key

Foreign Key

Check part key

dependency: We note that

description, price, and taxdepend on part of the key

( Item code) not on full key

( item code+ invoiceno) so

remove these data item

into new table.

2NF

Invoice

Invoice_No

Invoice_date

Customer_No

Customer_Name

Customer_Address

Tax_total

Gross_Total

Net_Total

Item

Item_code

Item_Description

Price

Tax_percent

Invoice_Item

Invoice_No

Item_Code

Quantity

Tax_amount

Net_amount

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UNF 1NF 2NF

Invoice

Invoice_No Invoice Invoice_No

Invoice_date Invoice_No Invoice_date

Coustomer_no Invoice_date Customer_no

Customer_Name Customer_no Customer_Name

Customer_Address Customer_Name Customer_Address

Tax_total Customer_Address Tax_total

Gross_Total Tax_total Gross_Total

Net_Total Gross_Total Net_Total

Item_code Net_Total Item

Item_Description Item Item_code

Price Invoice_No Item_Description

Quantity Item_code Price

Tax_percent Item_Description Tax_percent

Tax_amount Price Invoice_Item

Net_amount Quantity Invoice_No

Tax_percent Item_code

Tax_amount Quantity

Net_amount Tax_amount

Net_amount Primary Key

Foreign Key

Check none key dependency:

We note that customer

name, customer address

depends oncustomer No. so we create a

new data group with primary

key customer No. all other

data groups

are fully dependent on

primary key, so no change

will take place.

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Summary

• 1NF

• A relation is in 1NF if it contains no repeating groups

• To convert an unnormalised relation to 1NF either:

•

Flatten the table and change the primary key, or• Decompose the relation into smaller relations, one for

the repeating groups and one for the non-repeating

groups.

•

Remember to put the primary key from the originalrelation into both new relations.

• This option is liable to give the best results.40

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Summary

• 2NF

• A relation is in 2NF if it contains no repeating groups and no

partial key functional dependencies

• Rule: A relation in 1NF with a single key field must be in 2NF

•To convert a relation with partial functional dependencies to 2NF.create a set of new relations:

• One relation for the attributes those are fully dependent upon

the key.

• One relation for each part of the key that has partially dependent

attributes

41

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Summary

• 3NF

• A relation is in 3NF if it contains no repeating groups, no partial

functional dependencies, and no transitive functional

dependencies

•

To convert a relation with transitive functional dependencies to3NF, remove the attributes involved in the transitive dependency

and put them in a new relation

• Rule: A relation in 2NF with only one non-key attribute must be in

3NF

•

In a normalized relation a non-key field must provide a fact aboutthe key, the whole key and nothing but the key.

• Relations in 3NF are sufficient for most practical database design

problems. However, 3NF does not guarantee that all anomalies

have been removed.42

ITDB 1102-Chapter4

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