Lect#5 - Normalization.ppt

7/23/2019 Lect#5 - Normalization.ppt

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Normalization

Pearson Education Limited 1995, 2005


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Objectives2

What is normalization and the purpose ofnormalization

What is update anomalies? How normal forms can be transformed

from lower normal forms to highernormal forms; 1NF, 2NF and 3NF



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Purpose of

Normalization3

Normalization is a techniue of anal!zing and correcting tablestructure for producing a set of suitable relations that supportthe data reuirements of an enterprise" #esult$ a set of relations with minimized data redundancies

%haracteristics of a suitable set of relations include$ the minimalnumber of attributes necessar! to support the

data reuirements of the enterprise;

attributes with a close logical relationship are found in thesame relation i"e each table represent a single sub&ect

minimalredundanc! with each attribute represented onl!once with the important e'ception of attributes that form allor part of foreign (e!s i"e no data item will be unnecessaril!stored in more than 1 table

)ll attributes in a table are dependant on the primar! (e!



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Purpose of

Normalization4

*he bene+ts of using a database that hasa suitable set of relations is that thedatabase will be$ easier for the user to access and maintain

the data reducing the opportunities fordata inconsistencies;

ta(e up minimal storage space on thecomputer"



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How NormalizationSupports Database Design5



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Data Redundancy andUpdate nomalies6 a&or aim of relational database design

-i"e normalization. is to group attributesinto relations to minimize data

redundanc! /roblems associated with data

redundanc! are illustrated b! comparing

the Staffand Branchrelations with theStaffBranchrelation"



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Data Redundancy andUpdate nomalies7


Design 1

Design 2

D R d d d U d


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Data Redundancy and Updatenomalies

8

StaffBranchrelation has redundant data; thedetails of a branch are repeated for e0er!member of sta" -#efer to esign 2.

n contrast, the branch information -bAddress.appears onl! once for each branch in the

Branchrelation and onl! the branch number-branchNo. is repeated in the Staff relation,to represent where each member of sta islocated" -#efer to esign 1.

#elations that contain redundant information

ma! potentiall! suer from update anomalies" *!pes of update anomalies include

nsertion eletion

odi+cation Pearson Education Limited 1995, 2005


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!nsertion nomalies "

#$amples9

f esign 2is used, to enter the details of new sta with branch no" 4556

would reuire that the correct details of branch no" 4556is entered so that it will be consistent with 0alues for

branch no" 4556 in other tuples" 4ut if esign 1 relationis used, the! do not suer this potential inconsistenc! to insert a new branch that has no member, other

attributes would consist null 0alues 7 this can 0iolateprimar! (e! re"


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Deletion nomalies "

#$ample10

f esign 2 is used, if we delete a tuple fromthe relation that represents the last memberof sta located at a branch -branchNO8

4556., the details of the branch is lostcompared to if we used the relations Staffand Branch relationsin esign 1"


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%odi&cation nomalies "#$ample11

f esign 2 is used, if the 0alue of theattribute is to be changed for e'amplebAddress = 22 eer #d, 9ondon, the

other tuples with the same bAddressmustalso be updated"


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'(e Need forNormalization12:'ample$ %ompan! that manages building

pro&ects :ach pro&ect has its own pro&ect number, name,

emplo!ees assigned to it

:ach emplo!ee has an emplo!ee number, name &ob classi+cation

%harges its clients b! billing hours spent oneach contract

Hourl! billing rate is dependent on emplo!ee


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'(e Need for Normalization

)continued*13


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'(e Need for Normalization)continued*

14

>tructure of data set in pre0ious +guredoes not handle data 0er! well odi+cation anomalies nsertion anomalies eletion anomalies


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'(e NormalizationProcess15Wor(s through a series of stages called

normal forms$ nnormalized form -NF. 7 ) table that contain

one or more repeating groups First normal form -1NF. 7 table format; no

repeating group

>econd normal form -2NF. 7 1NF and no partial

dependencies *hird normal form -3NF. 7 2NF and no transiti0e

dependencies


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'(e Process of

Normalization16



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+onversion to ,irst

Normal ,orm17

#epeating group eri0es its name from the fact that a group of

multiple entries of same t!pe can e'ist for an!single (e! attribute occurrence

:'" PROJ_NUM81= has = entries that arerelated because the! each share thePROJ_NUM81= characteristics

#elational table must not contain repeating

groups 8@ reAecting data redundancies Normalizing table structure will reduce data

redundancies


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+onversion to

-N,)continued*18

>tep 1$ :liminate the #epeating Broups /resent data in tabular format, where each

cell has single 0alue and there are no

repeating groups :liminate repeating groups, eliminate nulls

b! ma(ing sure that each repeating groupattribute contains an appropriate data

0alue


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+onversion to

-N,)continued*19


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+onversion to

-N,)continued*20

>tep 2$ dentif! )ll ependencies

De&nition. ) functional dependenc!occurs when one attribute in a relationuniuel! determines another attribute"

*his can be written ) 4 which wouldbe the same as stating C4 is functionall!

dependent upon )C or C) determines4C"


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+onversion to

-N,)continued*21

ependencies can be depicted with help ofa diagram -or dependenc! notation ) 4."

ependenc! diagram$

epicts all dependencies found within gi0entable structure

Helpful in getting bird


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+onversion to

-N,)continued*

/artial dependenc!7 a dependenc! that that is based on onl!part of a composite primar! (e!

*ransiti0e dependenc!7 a dependenc! of one nonEprimeattribute on another nonEprime attribute

22


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+onversion to

-N,)continued*23

>tep 3$ dentif! the /rimar! e! /rimar! (e! must uniuel! identif!

attribute 0alue" n other words, if a 0alue

of the (e! is gi0en, onl! one answer canbe returned for other attributes" For e'ample, PROJ_NUM in the sample

schema cannot be a primar! (e!" *his is so

since PROJ_NUM81= can identif! an! one of =emplo!ees so PROJ_NUMalone is not enoughto be used as a primar! (e!


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+onversion to

-N,)continued*24

/rimar! (e! can be determined based onthe functional dependencies identi+edearlier"

t can be a single attribute, i"e", thedeterminant which can determine uniuel! allattributes or

%omposition of se0eral determinants which

can co0er all attributes" GNote$ if there are fewpossibilities, choose the ones with biggestscope


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+onversion to

-N,)continued*

/rimar! (e! is combination of pro&Inum and empInum"

25


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Result of -N,26

#esult from 1NF normalization process will beone relation with all attributes listed"/rimar!Jcomposite (e! is underlined"

:'ample$

:/9KL::I/#KM:%* -pro&Inum, pro&Iname,empInum,

empIname, &obIclass,chgIhr, hours.Relation name

Primary/composite

key

All attributes


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-N,27

n First normal form $ )ll (e! attributes are de+ned *here are no repeating groups in the table that is

each rowJcolumn intersection contains one andonl! one 0alue, not a set of 0alues

)ll attributes are dependent on primar! (e! /roblem$ 1NF table structure contains partial

dependencies

>ometimes used for performance reasons, butshould be used with caution

>till sub&ect to dataredundancies" :'" Whathappen if EMP_NUM 8 15= changes JOB_CLASS?


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+onversion to Second

Normal ,orm28

#elational database design can be impro0ed b!con0erting the database into 2NF"

2NF remo0es partial dependenc!

f 1NF relation has a single attribute as primar!(e!, then the relation is automaticall! in its 2NFas well"

/artial dependenc! can onl! happen when

composite (e! e'ists" f we ha0e more than oneattribute in the (e!, then there are possibilitiesthat some attributes ma! depend on a portionof the (e! onl!"


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+onversion to0N,)continued*29

Step -$ Write :ach e! %omponent on a>eparate 9ine

Write each (e! component on separate line,

then write original -composite. (e! on last linePROJ_NUM

EMP_NUM

PROJ_NUM EMP_NUM

:ach component will become (e! in newtableJrelation

!"E# $% t&e key &as 2 attributes 'A,(), t&en possible components *ill

be A, (, and A(+ $% components 'A,(,-), t&en it *ill be A, (, -, A(,

A-, (- and A(-+


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+onversion to 0N,)continued*30Step 0. )ssign %orresponding ependent )ttributes etermine those attributes that are dependent on

other attributes(PROJ_NUM, PROJ_NAME)

(EMP_NUM, EMP_NAME, JOB_CLASS, CHG_HOUR)

(PROJ_NUM, EMP_NUM, HOURS)

)t this point, most anomalies ha0e beeneliminatedPROJECT(PROJ_NUM, PROJ_NAME)

EMPLOYEE(EMP_NUM, EMP_NAME, JOB_CLASS, CHG_HOUR)

ASSIGNMENT(PROJ_NUM, EMP_NUM, HOURS)


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+onversion to

0N,)continued*31

f at the end, there are relations withonl! the (e!s in them -e'cept for therelation ha0ing all (e!s., then the

relations can be eliminated" #elation is in second normal form -2NF.

when it includes no partial dependencies


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not(er tec(ni1ue toconvert to 0N,32

Step -. Write the original 1NF relation:/9KL::I/#KM:%* -pro&Inum, pro&Iname, empInum,

empIname, &obIclass, chgIhr, hours.

Step 0. For each partial dependenc!, create a newrelation, with the determinant as (e!" n the 1NF,delete the dependents and circleJitalicJcolored the(e! -foreign (e!."

:/9KL::I/#KM:%* -pro&Inum, empInum,

empIname, &obIclass, chgIhr, hours.

/#KM:%* -pro&Inum, pro&Iname.

Pro.num

pro.name

#e eat for other artial


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Result of 0N,33

#esult from 2NF normalization process will bemultiple relations" :ach primar!Jcomposite (e!is underlined" :ach foreign (e! identi+ed-circleJitalicJcolored.

:'ample$

:/9KL::I/#KM:%* -pro&Inum, empInum,hours.

/#KM:%* -pro&Inum, pro&Iname

:/9KL:: -empInum, empIname, &obIclass,chgIhr.


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+onversion to

0N,)continued*34


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+onversion to '(irdNormal ,orm35 3NF remo0es transiti0e dependenc!

>tep 1$ Write the pre0ious 2NF relations

>tep 2$ For each transiti0e dependenc! -nonE(e! dependents on another nonE(e!., createa new relation with determinant as (e!"

>tep 3$ n the original 2NF, delete thedependents" a(e the (e! into foreign (e!-circleJitalicJcolored."


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Result of 2N,36

#esult from 3NF normalization process will bemultiple relations" :ach primar!Jcomposite (e!is underlined" :ach foreign (e! identi+ed-circleJitalicJcolored.

:'ample$

:/9KL::I/#KM:%* -pro&Inum, empInum,hours.

/#KM:%* -pro&Inum, pro&Iname

:/9KL:: -empInum, empIname, &obIclass.

MK4 -&obIclass, chgIhr.ee t&e di%%erence+ $n 2, t&e key is bot&

%+k+ and p+k+ $n , t&e key is %+k+ only


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+onversion to 2N,

)continued*

Note$ Kriginal EMPLOYEEtable


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staffNo branchNo branchAddress name position hoursPerWeek

S4552 B001 City South Plaza, Seattle, WA98122

Ellen London Assistant 16

S4555 B004 16 14th A!enue, Seattle, WA98128

Ellen Lay"an Assistant 9

S4612 B002 City Cente# Plaza, Seattle,WA 98122

$a!e Sin%lai# Cle#& 14

S4612 B004 16 14th A!enue, Seattle, WA

98128

$a!e Sin%lai# Cle#& 10

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E'a"ine the ta(le sho)n a(o!e* +his ta(le #e#esents the hou#s )o#&ed e# )ee&

-o# te"o#a#y sta-- at ea%h (#an%h o- a %o"any*

1* .denti-y the -un%tional deenden%ies #e#esented (y the data sho)n in the

ta(le*

2* /sin the -un%tional deenden%ies identi-ied in a#t 2, des%#i(e and illust#ate

the #o%ess o- no#"alization (y %on!e#tin the ta(le to +hi#d 3o#"al o#" 3

#elations* .denti-y the #i"a#y and -o#ein &eys in you# 3 #elations*

Sample #$ercise-


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i!en the -ollo)in #elational s%he"a7

MOVIE(cinemaID, cinemaCapacit, mo!ieID, mo!ie"it#e, mo!ieDuration,sho$Date, sho$"ime, actorID, actorName, ticketPrice, ticket%o#d,tota#Co##ection&

1* S&et%h a ta(le )ith the att#i(utes o- the a(o!e s%he"a as %olu"n heade#s*

Poulate the ta(le )ith 10 #e%o#ds o- data*

2* .denti-y the #i"a#y &ey and the -un%tional deenden%ies #e#esented (y the

data sho)n in the ta(le*

* /sin the -un%tional deenden%ies identi-ied in a#t 2, des%#i(e and illust#ate

the #o%ess o- no#"alization (y %on!e#tin the ta(le to +hi#d 3o#"al o#" 3

#elations* .denti-y the #i"a#y and -o#ein &eys in you# 3 #elations*

Sample #$ercise0


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40

i!en the -ollo)in in%o"lete deenden%y dia#a",

a $#a) an a##o) -o# ea%h -un%tional deenden%y

( State the #i"a#y &ey (ased on the identi-ied -un%tional deenden%ies

% W#ite the 13 #elational s%he"a -o# the dia#a"

d .denti-y any a#tial deenden%y

e 3o#"alize the #elation in % into 23 #elations

- .denti-y any t#ansiti!e deenden%y

3o#"alize the #elation in e into 3 #elations*

Sample #$ercise2

'#%!D

+'R3

4RP

%'+H

!D

D'#

'!%#

S'D!U%

5O+ 6 5 D 4, 4 P'


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5earning Outcomes41

Now students should be able to$ :'plain what is normalization and the

purpose of normalization

/erform normalization process fromlower normal forms to higher normalforms; 1NF, 2NF and 3NF


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References42

Database Systems 7 practical pproac( toDesign8 !mplementation and %anagement9

Thomas Connolly, Carolyn Begg (2010), AddisionWesley, Fifth Edition.

Chapter 1

Database Systems Design, Implementation& Management.

!eter "o#, Carlos Coronel (200$), Thomson Co%rseTe&hnology, 'eenth edition.

Chapter (pg 1* + 1*)

Documents

Lect#5 - Normalization.ppt