COMP283-Lecture5

AppliedDatabaseManagement

Introduction

DatabaseAdministration Optimisation

Normalisation

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Comp283-Lecture5Optimisation:DBKeys

● UniqueConstraints● Enforcesuniquenessonthesetofattributesdefinedinthem.

● Onlyonerowcancontainnull● PrimaryKeys● specialcaseofauniqueconstraint● oneormorecolumnsthattogetheruniquelydefinetherecord

● tablecanonlyhaveoneprimarykey● usually(andshouldbe)indexed● Everytableshouldhaveaprimarykey �2

Comp283-Lecture5Optimisation:DBKeys● ForeignKey●Whenarelationshipexistsbetweentwotablesbasedonsomecommonsetofattributes,theintegrityofthedatacanbeenforcedbydefiningaForeignKey.

● Thereisoneprimarytableandonesecondary.● Setofattributesinsecondaryreferencingakeyintheprimarytable

● Attributesandstructureoflinked-to-keyinPrimarycannotbemodified(thoughdatacanofcourse)

● CompositeKey● auniqueconstraintmadeupofmultiplecolumns.

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Comp283-Lecture5

Optimisation:DBIndexes● ClusteredIndexes● Eachtablecanhaveamaximumof1clusteredindex● Defineshowthedatabasewillsortthetable’sdata.● Aclusteredindexisastored(on-disk)structureassociatedwithaspecifictableorview,designedtohelpspeedupdataretrieval.

● Automaticallycreatedwhenaprimarykeyisdefined.Sinceeverytableshouldhaveaprimarykey,everytablewillhaveaclusteredindex.

● Un-ClusteredIndexes● Additionalindexes(ifyouchoosetomakethem)areunclustered.

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Comp283-Lecture5

Optimisation:DBIndexes:ClusteredIndexes

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Record 04

Record 02

Record 06

Record 05

Record 01

Record 03

Indexed by Primary Key

Record 04

Record 02

Record 06

Record 05

Record 01

Record 03

Comp283-Lecture5

Optimisation:DBIndexes:ClusteredIndexes

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R4

R2 R6 R5 R1 R3

1 2 3 4 5 6

Record 04

Record 02

Record 06

Record 05

Record 01

Record 03

Indexed by Primary Key

Comp283-Lecture5

Optimisation:DBIndexes:Un-clusteredIndexes

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R4

R2 R6 R5 R1 R3

2 4 1 5 6 3Indexed by some other Key

Record 04

Record 06

Record 05

Record 03

Record 02

Record 01

Comp283-Lecture5Optimisation:TablePartitioning● UsedforLargedatabases.● TablePartitioningcutsupthetableintosmallermoremanageablesizes.

● TheDBMSperformsPartitioninginthebackground.● Improvesperformanceforqueriesonsmallsubsetsofdata.● HardwarePartitioning● HorizontalPartitioning● VerticalPartitioning● Normalisation● RowSplitting

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Comp283-Lecture5DBStorage:NormalisationForms● Normalisationistheprocessoftakingallofthedatathatistobestoredinadatabaseandseparatingitintodistincttablesfollowingstrictrulestoproducethemostefficientdatabasestoragestructure.

● Entityintegrity● Eachrowofatableisconsistent,generallyitshouldrepresentasetofuniqueattributes(thusitisaTuple)structuredsothateachattributerepresentsmeaningfortheobject

● Domainintegrity● Eachcolumnofatableisconsistent-alldatainthecolumnconformstothedefinitionoftheattribute.Aconstraintcanbeplacedonthecolumntoforcedomainintegrity.E.g.youcanallowordisallowNullvalues,definearangewithinwhichthedatavaluemustexist,theformatofthedata,aswellasspecifyingthedata-type.

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Comp283-Lecture5DBStorage:NormalisationForms● Referentialintegrity● Maintainthedataconsistencybetweencolumnsinatableandalsobetweenrelatedtablesinthedatabase.Oftenenforcedusingaforeignkeywhichassociatesthedataattributeswithdataattributesinanothertable.

● User-definedintegrity● Maintaindataconsistencybystipulatingotherspecificrules.Usuallyenforcedusingstoredproceduresandtriggers.e.g.youmayrequirealogtabletobeupdatedwithareferencetoadatainsert,recordingtheuserthatmadetheinsert-Canbedoneusingatriggeronthedatatablethatcausessomecodetobeexecutedtoupdatethelogtable.

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Comp283-Lecture5DBStorage:1NF● TheFirstNormalForm(1NF)● Thetablesmustnothaveanyduplicaterecords,creatingaprimarykeyonthetablewillsatisfythisrule.

● Notwocolumnsinthetableshoulddescribethesameattributetype.e.g.inabankingsystem;Current,Savings,Loancolumnsarealldescribingbankaccounttypes.

● Entriesinacolumnmustbeofthesamedata-type.● Eachrowmustcontainthesamenumberofcolumns(eachrecord/tuplehasthesamenumberandtypeofattributes–justdifferentvalues)

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Comp283-Lecture5DBStorage:2NF● TheSecondNormalForm(2NF)● Mustbein1NF● Anynon-candidatekeyattributemustbedependantonthewholeofthePrimaryKey.

● e.g.● {Flight_No,Date,Safety_Check,Destination}Fails

2NF● But● {Flight_No,Date,Safety_Check}and {Flight_No,Destination} Passes2NF

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Comp283-Lecture5DBStorage:2NF

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Flight_No Date Safety_Check DestinationBA32765 21/05/2017 Full-OK-03632 BelfastBA32765 22/05/2017 Full-OK-03784 BelfastLH93162 22/05/2017 Part-OK-73291 BerlinBA32765 23/05/2017 Full-OK-26534 Belfast

Flight_No Date Safety_CheckBA32765 21/05/2017 Full-OK-03632BA32765 22/05/2017 Full-OK-03784LH93162 22/05/2017 Part-OK-73291BA32765 23/05/2017 Full-OK-26534

Flight_No DestinationBA32765 BelfastLH93162 Berlin

Comp283-Lecture5DBStorage:3NF● TheThirdNormalForm(3NF)● Mustbein1NF&in2NF.● Thetablesmustonlycontainnon-primarykeyattributesthatarefullydependantonthePrimaryKey.

● e.g.● {Flight_No,Date,Gate_No,Gate_Supervisor}Fails3NF,succeeds1NFand2NF

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● {Flight_No,Date,Gate_No}and {Gate_No,Date,Gate_Supervisor}arein3NF

Comp283-Lecture5DBStorage:3NF

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Flight_No Date Gate_No Gate_Supervisor

BA32765 21/05/2017 12 Mr Jones

BA32765 22/05/2017 12 Ms Smith

LH93162 22/05/2017 8 Mr Jones

BA32765 23/05/2017 12 Ms Brown

Comp283-Lecture5DBStorage:3NF

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Flight_No Date Gate_No

BA32765 21/05/2017 12

BA32765 22/05/2017 12

LH93162 22/05/2017 8

BA32765 23/05/2017 12

Date Gate_No Gate_Supervisor

21/05/2017 12 Mr Jones

22/05/2017 12 Ms Smith

22/05/2017 8 Mr Jones

23/05/2017 12 Ms Brown

● OurDateattributeswouldactuallybeDateandTimeofcourse-unlessweonlyhadoneflightperdaypergate!

Comp283-Lecture5DBStorage:4NF● TheFourthNormalForm(4NF)● Mustbein1NFandin2NFandin3NF.● Thetablesmustcontainonlyoneindependentmulti-valuedfactabouttheentity.● e.g.{Person,CarReg,PetName} Fails4NFApersoncouldownmorethan1carandcouldownmorethan1pet,butcarsandpetsarenotdependentoneachother.

● Howdowerecordthis?

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Comp283-Lecture5DBStorage:4NF-continued● Possiblesolutionsfor{Person,Cars,Pets}

Person Cars Pets

Fred LamborghiniGallardo

Fred PrinceRupert1(dog)

Fred Mollie(cat)

Fred Citroen2CVPerson Cars Pets

Fred LamborghiniGallardo PrinceRupert1(dog)

Fred Citroen2CV Mollie(cat)

Person Cars Pets

Fred LamborghiniGallardo PrinceRupert1(dog)

Fred Citroen2CV PrinceRupert1(dog)

Fred LamborghiniGallardo Mollie(cat)

Fred Citroen2CV Mollie(cat)

Orconformto4NF:

{Person,Cars}and {Person,Pets}

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Comp283-Lecture5DBStorage:5NF● TheFifthNormalForm(5NF)● Mustbein1NF,in2NF,3NFandin4NF.● Aspecialisationof4NF.● Inthiscasesomeexternalrulegovernstherelationshipofthefactstotheentity● e.g.{Salesman,Manufacturer,Products} Rule:AsalespersonauthorisedtosellproductsoftypeAandalsoauthorisedtosellanyproductfromManufacturerB,mustbeabletosellanyproductoftypeAmadebymanufacturerB.

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Comp283-Lecture5DBStorage:5NF-Continued

Salesman Manufacturer Product

Fred Phillips TV

Jane Phillips Amplifiers

Jane BOSE Speakers

Joe Sony TV

Joe Sony Amplifiers

{Salesman,Manufacturer,Products} Rule:AsalespersonauthorisedtosellproductsoftypeAandalsoauthorisedtosellanyproductfromManufacturerB,mustbeabletosellanyproductoftypeAmadebymanufacturerB.

Salesman Product

Fred TV

Jane Amplifiers

Jane Speakers

Joe TV

Joe Amplifiers

Salesman Manufacturer

Fred Phillips

Jane Phillips

Jane BOSE

Joe Sony

Manufacturer Product

Phillips TV

Phillips Amplifiers

BOSE Speakers

Sony TV

Sony Amplifiers

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COMP283-Lecture5

Conclusion● DatabaseKeys● Normalisation

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