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Database Systems and

Applications

Lecture 15

Normalization

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Normalization & Normal form

NormalizationIt is a tool to validate and improve t logicaldesign, so that it satisfies certainconditions that avoid unnecessary

duplication of data.It is based on the analysis of functionaldependencies.

Normal form

It is a state of relation that results byapplying simple rules regarding functionaldependencies (or relationships betweenattributes) to that relation.

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Normalization is often executed as aseries of steps. Each stepcorresponds to a specific normal formthat has known properties.

As normalization proceeds, therelations become progressively morerestricted in format, and also less

vulnerable to update anomalies. For the relational data model, it isimportant to recognize that it is onlyfirst normal form (1NF) that is critical

in creating relations. All the

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Update Anomalies

Relations that have redundant datamay have problems called update

anomalies, which are classified as ,

Insertion anomaliesDeletion anomalies

Modification anomalies

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Steps in normalizationTable with multi-valued attributes

1st normal form

2nd normal form

3rd normal form

Boyce-Coddnormal form

4th normal form

5th normal form

Remove multi-valued attributes

Remove partialdependencies

Removeremaining anomalies

resulting from functionaldependencies

Remove transitive

dependencies

Remove multi-valued dependencies

Remove remaining

anomalies

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Definition of 1NF

First Normal Form is a relation in which the intersection of each

row and column contains one and only one value.

There are two approaches to removing repeating groups from

unnormalized tables:

1. Removes the repeating groups by entering appropriate

data in the empty columns of rows containing the repeating

data.

2. Removes the repeating group by placing the repeatingdata, along with a copy of the original key attribute(s), in a

separate relation. A primary key is identified for the new

relation.

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First Normal Form (1NF)

A relation is in 1NF if it contains nomulti valued attributes. Ex: st_id name h_no r_no c_no year

sem grade

2009P7PS001 Venu BH1 005 CSGC 210 2010-11

2 ACSGC222 2010-11

2 B

2009P7PS020 Amit BH2 068 CSGC210 2010-112 B

CSGC230 2010-112 A

EEGC245 2010-

11 2 A

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1NF (cont.)

Ex:

st_id name h_no r_no c_no year

sem grade2009P7PS001 Venu BH1 005 CSGC210 2010-11

2 A

2009P7PS001 Venu BH1 005 CSGC222 2010-11

2 B2009P7PS020 Amit BH2 068 CSGC210 2010-11

2 B

2009P7PS020 Amit BH2 068 CSGC230 2010-112 A

2009P7PS020 Amit BH2 068 EEGC245 2010-11

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Full functional dependency

Full functional dependency indicates that if A and B

are attributes of a relation, B is fully functionally

dependent on A if B is functionally dependent on A,

but not on any proper subset of A.

A functional dependency AB is partially dependentif

there are some attributes that can be removed from A and

the dependency still holds.

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Second Normal Form (2NF)

A relation is in 2NF if it is in 1NFand every non key attribute isfully functionally dependent on

the primary key.

i.e., no non key attribute isfunctionally dependent on part(but not all) of the primary key.

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2NF (cont.)

A relation that is in 1NF will be in 2NFif any one of the following conditionsapplies:

The primary key consists of onlyone attribute (st_id in STUDENT1).

No non key attributes exist in therelation (i.e., all the attributes arepart of the primary key in therelation)

Every non key attribute is

functionally dependent on the full

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Examples

st_id st_name h_no r_no address

STUDENT1

STUDENT2

st_id c_no st_name h_no r_no address sem year grade

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2NF (cont.)

The relation STUDENT2 is not in2NF.

The primary key in this relation iscomposite key st_id, c_no.

In this the nonkey attributesname, h_no, r_no, address arefunctionally dependent on part of

the primary key (st_id) but not onc no.

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2NF (contd.)

A partial functional dependencyis a functional dependency inwhich one or more non key

attributes are functionallydependent on part of the primarykey.

For example, in STUDENT2, thepartial dependency creates

redundancy. It leads to

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2NF (cont.)

In this example

the redundancy is the attributesname, h_no and r_no will appear inall the rows of the student hastaken courses

when there is change in h_no and/orr_no, we have to update it in morethan one row depending upon thenumber of courses a student hastaken. The anomaly may occur even

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2NF (cont.)

So to convert a relation to 2NF, it is necessaryto decompose the relation into new relationsthat satisfy one (or more) of the previouslydescribed conditions.

Ex : We shall decompose the relationSTUDENT2 into two relations.

STUDENT1(st_id, name, h_no, r_no, adddress) ST_COURSE(st_id, c_no, sem, year, grade)

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If a relation cant be convertedto the second normal form, yourisk data redundancy and

difficulty in changing data. Toconvert first-normal-form tablesto second-normal-form tables,remove columns that are notdependent on the primary key.