9-DB-Normalization

8/7/2019 9-DB-Normalization

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In the name ofALLAH


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Introduction toDatabase Systems

Lecture 22

03-01-11

Fall 2010


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Department of Computer Science

Normalization

A step by step process to

produce more efficient and

accurate database design

Purpose is to produce ananomaly free design


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Anomalies

A state ofDB that can lead the DB

to inconsistency or incorrect state of

database

Four types of anomalies are of

concern here; Redundancy,

insertion, deletion and updation


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Normalization

A strongly recommended step

Normalized design makes the

maintenance of database easier

Normalization applied on each

table of a DB design


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Normalization

Performed after the logical

database design

Informally also performed

during conceptual DB design


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Normalization Process

Different forms or levels of normalization

Called first, second, third and so on

forms

Each form has got certain conditions

If a table fulfils the condition(s) for a

normal form then the table is in that

normal form


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Normalized DB Design

Process is applied on each table

The minimum form in which all tables

are in is called the normal form of the

entire database Objective is to place the DB in

highest form of normalization


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Functional Dependency

Normalization is based on

functional dependencies (FDs)

A type of relationship between

attributes of a relation


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Definition: IfA and B are attributes

of a relation R, then B isfunctionally dependent on A if each

value ofA in R is associated with

exactly one value ofB; written as

A B


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Functionally Dependency

It does not mean that A derives B,

although it may be the case sometime Means that if we know value ofA then

we can precisely determine a unique

value ofB


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Attribute of set of attributes on the left

side are called determinant and on theright are called dependents

Like R (a, b, c, d, e)

a b, c, d

d d, e


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FD Example

STD(stId, stName, stAdr, prName, credits)

stId stName, stAdr, prName, credits

prName credits


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In the name ofALLAH


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Lecture 23

06-01-11

Fall 2010


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FDs and Keys

A minimal super key is the

candidate key, so if adeterminant of an FD determines

all attributes of that relation then

it is definitely a super key, and


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FDs and Keys

If there is no other FD where a subset of

this determinant/SK is a super key, thenit is a candidate key

So FDs help to identify keys, how


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R(a, b, c, d, e, f, g)

a, c b, d, e, f, g

c d, e

a b, d, ff g, a, b, c, d, e


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FDs and Keys

EMP(eId, eName, eAdr, eDept, prId, prSal)

eId eName, eDept, eAdr

eId, prId prSalSTD(stId, stName, prName, adr, nic, cgpa)

stId stName, prName, adr, nic, cgpa

nic stName, prName, adr, stId, cgpa


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Inference Rules

Called inference axioms or armstrong

axioms These are rules that establish certain

FDs from a given set of FDs

These rules are sound


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Reflexivity

IfB is a subset ofA then A B,

it also implies that A A

always hold, that is

stName, stAdr stName

Or stName stName


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Augmentation

If we have A B then

AC BC that is

if stId stName then

stId, stA

drstName, st

Adr


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Transitivity

IfA B and BC then

A C

that is

If stId

prName and prNamecredits

Then stId credits


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Additivity or Union

IfA B and A C then ABC

if empId eName and empId qual

Then we can write it as

empId

eName, qual


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Projectivity or Decomposition

IfA BC then A B and ACif empId eName, qual


empId eName and empId qual


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Pseudotransitivity

IfA B and CB D then

AC Dif stId stName and

stName, fName stAdr


stId, fName stAdr


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Thanks


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In the name ofALLAH


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Lecture 24

10-01-11

Fall 2010


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Normal Forms


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First Normal Form

A relation is in first normal form

iff every attribute in every tuple

contains an atomic value

There is no multivaued(repeating group) in the relation


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First Normal Form

One of the basic properties of relation

Multiple values create problems inperforming different operations, like, select

or join

Remember the treatment of multivalued

attributes in the mapping process


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First Normal FormstId bkId stName stAdr prName

S1020 B00129 Sohail Dar I-8 Islamabad MCS

S1038 B00327 ShoaibAli G-6 Islamabad BCS

S1015 B08945 Tahira Ejaz L RukhWah MCS

S1015 B06352 Tahira Ejaz L RukhWah MCS

S1018 B08474 Arif Zia E-8, Islamabad. BIT

Mind the key please


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Second Normal Form

Full functional dependency: an

attribute B is fully functionallydependent on A if the B can be

determined by whole ofA not by

any proper subset ofA


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Full Functional Dependence

Consider the relation

CLASS(crId, stId, stName, fId, room, grade)

crId, stId stName, fId, room, grade

stId stName

crId fId, room


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Second Normal Form

A relation is in 2nd normal form iff it

is in the first normal form and allnon key attributes are fully

functionally dependent on key,

that is, there is no partialdependency


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Anomalies

crId stId stName fId room grade

C3456 S1020 Suhail Dar F2345 104 B

C5678 S1020 Suhail Dar F4567 106

C3456 S1038 M Shoaib F2345 104


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Second Normal Form

CLASS(crId, stId, stName, fId, room, grade)


stId

stName crId

fId, room


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Anomalies

Redundancy

Insertion Anomaly

Deletion Anomaly

UpdationA

omaly


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Anomalies

crId stId stName fId room grade

C3456 S1020 Suhail Dar F2345 104 B

C5678 S1020 Suhail Dar F4567 106

C3456 S1038 Shoaib Ali F2345 104 A

C5678 S1015 Tahira Ejaz F4567 106 B


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Second Normal Form

Relation is decomposed based on the FDsCLASS(crId, stId, stName, fId, room, grade)


stId stName crId fId, room

STD(stId, stName)

COURSE(crId, fId, room)

CLASS(crId, stId, grade)


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Second Normal Form

Each of these tables is insecond normal form

Free of anomalies due to partial

dependency


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Thanks


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Lecture 25

03-01-11

Fall 2010


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Third Normal Form

A table is in third normal form

(3NF) iff it is in 2NF and there isno transitive dependency, that

is, no non-key attribute is

dependent on another non-keyattribute


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Transitive Dependency

STD(stId, stName, stAdr, prName, prCrdts)

stId stName, stAdr, prName, prCrdtsprName prCrdts


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stId stName stAdr prName

S1020 Sohail Dar I-8 Islamabad MCS

S1038 ShoaibAli G-6 Islamabad BCS

S1015 Tahira Ejaz L RukhWah MCS

S1018 Arif Zia E-8, Islamabad. BIT


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prName prCrdts

MCS 68

BCS 132

BIT 134


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Third Normal Form

STD(stId, stName, stAdr, prName, prCrdts)

stId stName, stAdr, prName, prCrdts prName prCrdts

STD (stId, stName, stAdr, prName)

PROGRA

M (prName, prCrdts)


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3NF Relations

Each of the table is in 3NF Free of all anomalies


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Boyce-Codd Normal Form

A general form of 3NF

Every relation in BCNF is in 3NFvice-versa is not always true

3NF is checked in steps, BCNF

checked directly


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BCNF

A table is in BCNF if every

determinant is a candidate key

Situation when table in 3NF is

not in BCNF

A non-key determines a part of

the composite primary key


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BCNF

FACULTY(fId, dept, office, rank, dateHired)

fId, dept office, rank, dateHiredoffice dept

Table is in 3NF, not in BCNF since the office is not a

candidate key

Generates multiple overlapping candidate keys so wehave fId, office dept, rank, dateHired


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BCNF

We decompose the table again to

bring it into BCNFFACULTY (fId, dept, office, rank, dateHired)

FACULTY(fId, office, rank, dateHred)

OFFICE(office, dept)


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HigherNormal Forms

AfterBCNF fourth, fifth and domain-

key normal forms exist 4NF deals with multivalued

dependency, fifth deals with possible

lossless decompositions,D

KNFreduces further chances of any

possible inconsistency


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Consistent hardwork is major

key for success in life

9-DB-Normalization

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