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DesigningaDatabaseApplicationinVB6.0AbstractBeforeyoustarttodesignadatabase,itsimportantyouunderstandexactlywhatadatabaseisandwhattypesofdatabasesyouhavetochoosefrom.Theapplicationtypewillaffectthedatabasetypethatyouchoose.WhatIsaDatabaseAdatabaseisreallyasystemthatcontainsmanydifferentobjectsusedtogethertoallowyourapplicationfastandefficientaccesstothedata.Youcanusemanyexamplesofdatabaseswithyourapplication.ThemostcommonoftheseareasfollowsMicrosoftAccessMicrosoftFoxProOraclePersonalEdition7ior8iandMSSQLServer7.00isonlyafewtomention.Allthesedatabasescanrunonastandalonecomputerandallowyoutocreateverycomplexdatabasesforyourapplications.Pickingtherightdatabaseforyourapplicationisextremelyimportant,becausethewrongonewillaffectperformanceandmakeyourjobasadevelopersomuchmoredifficult.Beforestartingthedesignprocess,youneedtoselectadatabase.WhenworkingwithVisualBasic,thedatabasethatyoucanchoosefromfallintotwodistinctgroupsLocalDatabasescanbeaccesseddirectlyfromVisualBasicthroughVisualBasicsdatabaseJetengineandRemotedatabasescannotbeaccessedbyusingVisualBasicsstandarddatabaseaccesscapabilities.Understandingthedifferenceswillhelpyouselectthecorrectdatabaseforyourapplication.However,inVisualBasic6,thereisnowawaytoaccessbothlocalandremotedatabasesusingthesamedatabaseaccesscontrolsandobjectsknownastheActiveXDataObjects.UnderstandingUniversalDataAccessUDAAsdatabaseshavegrownandmovedoffthelocalcomputerandontonetworkeddatabaseservers,themethodsemployedtoaccessthedatabaseshavechanged.Microsofthasaddressedthesechangesbydevelopingstrategytoallowforanycompanyordatabasetobeaccessedthesameway.ThisiscalledUniversalDataAccess,orUDA.UnderstandingwhatUDAmeansisnotassimpleasunderstandingtouseit.ThereasonforthisisthatUDAisasetofrulesandaccessmethodsthatmustbefollowedbyanycompanythatiscreatingadatabaseaccessmethodtobeused.Thisallowsyou,theprogrammer,toaccessanydatabasethesamewayButwhatisUDAUniversalDataAccessisaplatform,applicationsandtoolsconceptthatMicrosofthasdevelopedthatdefinesanddeliversthestandardsforallfutureapplicationdevelopment.UsingUDAstandardswillprovidehighperformanceaccesstomanytypesofdataandinformationthatresideonmultipleplatforms,andaprogramminginterfacethatwillworkwithalmostanytoolorlanguageusingtheskillsthatdevelopersalreadyhave.ThisisaccomplishedbyusingMicrosoftsDataAccessComponentsMDAC,aswellasanintegratedsetoftechnologies,whichincludeActiveXDataComponentsADO,OLEDB,andOpenDatabaseConnectivityODBC.ThebenefitsofusingthesestandardsincludethefollowingHighperformanceaccesstodata–ProvidestheabilitytoscaleanyapplicationorcomponenttosupportconcurrentlyconnecteduserswithoutlosingperformanceReliability–ReducesthenumberofcomponentstosupportontheclientPCandWideindustrysupport–ManyvendorsincludingMicrosofthavealreadyannouncedsupportfortheUDAstandards.InpreviousreleasesofVisualBasic,youneededtochoosefromeitherDAOlocalaccessmethodstodataorRDOremoteaccesstodata.Now,withthesupportofUDA,VisualBasichasathirdmethodfordataaccesscalledADO,orActiveXDataObjects.Thisallowsyoutocombinethedifferentwaysofaccessingdataintoonesetofprogrammingcallsandobjects.ADOworksinconjunctionwithOLEDBandODBCtoprovideaccesstoonedatabaseyoumightbeworkingwith.Gettingforward,MicrosoftplanstophaseoutODBCinfavourofOLEDBandtheUDAstandards.However,forthenearfuture,DAOandRDO,aswellasODBC,willstillbesupportedtoallowdeveloperstoslowlymoveuptothenewstandardsofdataaccess.LocalDatabasesLocaldatabasesaregenerallymuchsmallerthantheremotetypeofdatabase.ThefollowingdatabasesfallintothiscategoryMicrosoftAccessMicrosoftFoxProLotusWorksheetsMicrosoftExcelWorksheetsdBaseParadoxandASCII.Asyoucansee,thesePCresidentdatabasetypeshavebeenaroundforawhileandareavailablefromalmostanycomputersoftwarestore.AccessingthesedatabasesdoesntrequireanyothersoftwaretobeinstalledonthePC,nordoesitrequirespecialknowledgeonhowtoworkwiththem.However,thesizeoflocaldatabasesisrestricted.MicrosoftAccess97databasescantexceed1GBgigabyte.Localdatabasesaregenerallyusedforsingleuserapplicationssuchascheckbooks,addressbooks,andpersonalinformationmanagers.Someenterprisingteenagershavecreateddatabaseapplicationsthathelpthemkeeptrackofbaseballcardsorvideotapes.Soindecidingwhatyourapplicationwilladdressandhowitwillbeusedactuallyhelpsyouinthedatabaseselectionprocess.RemoteDatabasesBydefinitionremotedatabasesdontresideontheusersPC,butthisisnotalwaystrue.Infact,aremotedatabaseisanytypeofdatabasethatrequiresanODBCOpenDatabaseConnectivitydriverforanapplicationtoaccessit.ODBCdatabasesfallintotwomaincategoriesonethatrunonasinglePCandthelargercorporateonesthatrequirelarge,verypowerfulcomputerscalledserverswithlargeamountsofavailablediskspace.DatabaseserversareusedtoseparatetheworkloadbetweentheclientPCwheretheapplicationexecutesandthedatabasesystemwherethedatabasequeriesareperformed.ThisprovidestheapplicationwithfastdataaccesswithoutslowingdowntheusersPC.MostthelargeservertypedatabasesprovideversionsthatwillrunonstandalonePCs.MostlargecorporationsuseoneofthefollowingdatabasesystemsthoughthisisnottosaythatothersarentoutthereOracleSybaseandMicrosoftSQLServer.UsingaremotedatabaserequiresyoutouseeithertheremotedatabaseobjectsavailableonlyintheEnterpriseversionofVisualBasic6orthenewActiveXDataObjectsavailableinallreleasesofVisualBasic6.Ifyouredesigninganapplicationthatwilluseoneoftheselargedatabases,however,thebestwaytocreatetheapplicationthatwillusethesinglePCversionduringthedesign,developmentandtestingprocess.Then,wewhentheapplicationiscompleted,switchtoODBCconnectiontothelarger,serverbasedversion.BuildingtheInitialDesignCreatinganapplicationisalotlikebuildingahouse.Forawellbuilthouse,youneedablueprinttofollow,buttocreateagoodblueprint,youneedtoknowwhosgoingtoliveinthehouseandwhattheirlivingstyleswillbe.Thiswillhelpyoudecidethenumberandsizesofthebedrooms,whatcolourstouse,andsoon.Withanapplication,theblueprintisthetechnicalspecificationsthefunctionalspecificationsarewhatyouneedtoknowtocreatethetechnicalspecifications.Now,manybooksteachtheoverallapplicationdesignprocessbyusingverysimplisticexampleapplications.ThedescriptionoftheapplicationwemustdevelopisasfollowsPersonalAddress/PhoneBook–Thisapplicationwillkeeptrackofnames,addresses,andphonenumbersbyname.Itwillallowasmanydifferentaddressesandphonenumbersasneeded.Also,itwillallowtheentryofsomepersonalinformationsuchasbirthdate,spousesname,andchildrennamestobedeterminedlater.Itwillalsoprovidereportsinseveralformatsandallowuserstosearchthedatabaseforaparticularperson.ChoosingtheTasksDefiningtasksfortheapplicationalsodefinesitscomplexity.Forexample,thisapplicationisanaddress/phonebook,ifyoudecidetogiveuserstheabilitytoselectaphonenumberandhavethecomputerdialitforthem.Toaddthisfunctionalitytotheapplication,youneedtoknowhowtotestfortheexistenceofthemodem,connecttothatmodem,andthenactuallydialthatnumber.Ifyoudontknowhowtoaddthisfunctionality,youmightconsiderwaitingtoadditaftertheinitialversionoftheapplicationiscreatedandtested.Thisiswhatreleasingnewversionsareallabout.Keeptheinitialversionofthisapplicationatasimplerlevel.Thebestwaytodesignanapplicationistosaytoyourself,WhatwouldIwanttheapplicationtodoifIweretheuserBasically,yourethefirstandmostimportantuseroftheapplication.Thisapproachmightnotworkforthelarger,corporatetypeapplication,butitdoesworkforthesmaller,morepersonaltypes.Evenbeforeyoulistthedifferenttasksthattheapplicationwillperform,youneedtodecidewhattypeofapplicationinterfacetouseforthisapplication.Forthissampleapplication,usetheExplorerstyleinterface.Toreviewthisstyle,theinitialformthatusersseeandremaininformostoftheapplicationwillresembletheoneshowninFigure1.Figure1Thisinterfaceincludesmanyofthecontrolsthatyouhavelearnedearlier.Okay,wehavepickedtheapplicationthatyoullcreate–nowyouneedtolistthemainfunctionsthatitwillperform.Thinkofwhattheapplicationisforandthenlistwhatyouwantittodo.Fromthisreasoning,youshouldgetthefollowinglistKeepnamesandaddressesSearchforaparticularnamePrintdifferenttypesofreportsAllowfordifferentusersandEnableeasymaintenanceoftheapplication.Now,ifthislistseemssimplistic,itisYouwouldthenexpandeachiteminthislistuntilyouresatisfiedwiththeresult.Letsexpandeachoftheprecedingtasksandaddamoredetailtothedefinition.KeepingNamesandAddressesWhatdoyoureallymeanwhenyousayKeepnamesandaddressesItusuallymeansthatyouwanttokeeptrackofthestandardinformationfoundinanystandardtelephonebookyoulookat.Thefirststepindefiningalltheminitasksrequiredforthistopicistolistthedataelementsyouwanttoputinthedatabase.Table1liststhedataelementsthatyoucanuseforthistypeofapplication.NameTypeFirstNameStringLastNameStringSpouseNameStringChildNameStringAddressStringCityStringStateStringZIPIntegerEMailAddressStringPhoneLongBirthDateDateNotesStringTable1DataElementsThatCanBeIncludedInTheApplicationDatabase.
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