IT专业英语UNIT9 Database.ppt

UNIT9Database,9-1TechnicalPart9-2ReadingMaterial,9-1TechnicalPart9-1-1DefinitionAdatabaseisalsocalledanelectronicdatabase,referringtoanycollectionofdata,orinformation,thatisspeciallyorganizedforrapidsearchandretrievalbyacomputer.Adatabasehasthefollowingimplicitproperties:,Adatabaseisalogicallycoherentcollectionofdatawithsomeinherentmeaning.Arandomassortmentofdatacannotbereferredtoasadatabase.Adatabaseisdesigned,built,andpopulatewithdataforaspecificpurpose.Ithasanintendedgroupofusersandsomepreconceivedapplicationsinwhichtheseusersareinterested.Adatabaserepresentssomeaspectoftherealworld,sometimescalledtheminiworld.Changestotheminiworldarereflectedinthedatabase.,9-1-2IntroductionsDatabase-SystemApplicationsDatabasesarewidelyused.Herearesomerepresentativeapplications:1.EnterpriseInformationSales:forcustomer,product,andpurchaseinformation.Accounting:forpayments,receipts,accountbalances,assetsandotheraccountinginformation.Humanresources:forinformationaboutemployees,salaries,payrolltaxes,andbenefits,andforgenerationofpaychecks.,Manufacturing:formanagementofthesupplychainandfortrackingproductionofitemsinfactories,inventoriesofitemsinwarehousesandstores,andordersforitems.Onlineretailers:forsalesdatanotedaboveplusonlineordertracking,generationofrecommendationlists,andmaintenanceofonlineproductevaluations.,2.BankingandFinanceBanking:forcustomerinformation,accounts,loans,andbankingtransactions.Creditcardtransactions:forpurchasesoncreditcardsandgenerationofmonthlystatements.Finance:forstoringinformationaboutholdings,sales,andpurchasesoffinancialinstrumentssuchasstocksandbonds;alsoforstoringreal-timemarketdatatoenableonlinetradingbycustomersandautomatedtradingbythefirm.,3.Universities:forstudentinformation,courseregistrations,andgrades(inadditiontostandardenterpriseinformationsuchashumanresourcesandaccounting).4.Airlines:forreservationsandscheduleinformation.Airlineswereamongthefirsttousedatabasesinageographicallydistributedmanner.,5.Telecommunication:forkeepingrecordsofcallsmade,generatingmonthlybills,maintainingbalancesonprepaidcallingcards,andstoringinformationaboutthecommunicationnetworks.Asthelistillustrates,databasesformanessentialpartofeveryenterprisetoday,storingnotonlytypesofinformationthatarecommontomostenterprises,butalsoinformationthatisspecifictothecategoryoftheenterprise.,DataModelsUnderlyingthestructureofadatabaseisthedatamodel:acollectionofconceptualtoolsfordescribingdata,datarelationships,datasemantics,andconsistencyconstraints.Adatamodelprovidesawaytodescribethedesignofadatabaseatthephysical,logical,andviewlevels.Thereareanumberofdifferentdatamodels.Thedatamodelscanbeclassifiedintofollowingcategories:,1.RelationalModelTherelationalmodelusesacollectionoftablestorepresentbothdataandtherelationshipsamongthosedata.Eachtablehasmultiplecolumns,andeachcolumnhasauniquename.Tablesarealsoknownasrelations.Therelationalmodelisanexampleofarecord-basedmodel.Record-basedmodelsaresonamedbecausethedatabaseisstructuredinfixed-formatrecordsofseveraltypes.Eachtablecontainsrecordsofaparticulartype.Eachrecordtypedefinesafixednumberoffields,orattributes.Thecolumnsofthetablecorrespondtotheattributesoftherecordtype.Therelationaldatamodelisthemostwidelyuseddatamodel,andavastmajorityofcurrentdatabasesystemsarebasedontherelationalmodel.,2.Entity-RelationshipModelTheentity-relationship(E-R)datamodelusesacollectionofbasicobjects,calledentities,andrelationshipsamongtheseobjects.Anentityisa“thing”or“object”intherealworldthatisdistinguishablefromotherobjects.Theentity-relationshipmodeliswidelyusedindatabasedesign.,3.Object-BasedDataModelObject-orientedprogramming(especiallyinJava,C+,orC#)hasbecomethedominantsoftware-developmentmethodology.Thisledtothedevelopmentofanobject-orienteddatamodelthatcanbeseenasextendingtheE-Rmodelwithnotionsofencapsulation,methods(functions),andobjectidentity.Theobject-relationaldatamodelcombinesfeaturesoftheobject-orienteddatamodelandrelationaldatamodel.,4.SemistructuredDataModelThesemistructureddatamodelpermitsthespecificationofdatawhereindividualdataitemsofthesametypemayhavedifferentsetsofattributes.Thisisincontrasttothedatamodelsmentionedearlier,whereeverydataitemofaparticulartypemusthavethesamesetofattributes.TheExtensibleMarkupLanguage(XML)iswidelyusedtorepresentsemistructureddata.,5.XMLDatabaseAnXMLdatabaseisadatapersistencesoftwaresystemthatallowsdatatobestoredinXMLformat.Thisdatacanthenbequeried,exportedandserializedintothedesiredformat.XMLdatabasesareusuallyassociatedwithdocument-orienteddatabases.OConnellgivesonereasonfortheuseofXMLindatabases:theincreasinglycommonuseofXMLfordatatransport,whichhasmeantthat“dataisextractedfromdatabasesandputintoXMLdocumentsandvice-versa”.Itmayprovemoreefficient(intermsofconversioncosts)andeasiertostorethedatainXMLformat.,TwomajorclassesofXMLdatabaseexist:XML-enabled:thesemapallXMLtoatraditionaldatabase(suchasarelationaldatabase),acceptingXMLasinputandrenderingXMLasoutput.Thistermimpliesthatthedatabasedoestheconversionitself(asopposedtorelyingonmiddleware).NativeXML(NXD):theinternalmodelofsuchdatabasesdependsonXMLandusesXMLdocumentsasthefundamentalunitofstorage,whichare,however,notnecessarilystoredintheformoftextfiles.,6.MultimediaDatabaseMultimediadatatypicallymeansdigitalimages,audio,video,animationandgraphicstogetherwithtextdata.Theacquisition,generation,storageandprocessingofmultimediadataincomputersandtransmissionovernetworkshavegrowntremendouslyintherecentpast.,Thehugeamountofdataindifferentmultimedia-relatedapplicationswarrantedtohavedatabasesasdatabasesprovideconsistency,concurrency,integrity,securityandavailabilityofdata.Fromanuserperspective,databasesprovidefunctionalitiesfortheeasymanipulation,queryandretrievalofhighlyrelevantinformationfromhugecollectionsofstoreddata.,MultiMediaDatabases(MMDBs)havetocopeupwiththeincreasedusageofalargevolumeofmultimediadatabeingusedinvarioussoftwareapplications.Theapplicationsincludedigitallibraries,manufacturingandretailing,artandentertainment,journalismandsoon.Someinherentqualitiesofmultimediadatahavebothdirectandindirectinfluenceonthedesignanddevelopmentofamultimediadatabase.,MMDBsaresupposedtoprovidealmostallthefunctionalities,atraditionaldatabaseprovides.Apartfromthose,aMMDBhastoprovidesomenewandenhancedfunctionalitiesandfeatures.MMDBsarerequiredtoprovideunifiedframeworksforstoring,processing,retrieving,transmittingandpresentingavarietyofmediadatatypesinawidevarietyofformats.Atthesametime,theymustadheretonumericalconstraintsthatarenormallynotfoundintraditionaldatabases.,ConceptofDBMSAdatabasemanagementsystem(DBMS)isasoftwarepackagewithcomputerprogramsthatcontrolsthecreation,maintenance,anduseofadatabase.Itallowsorganizationstoconvenientlydevelopdatabasesforvariousapplications.Adatabaseisanintegratedcollectionofdatarecords,files,andotherobjects.ADBMSallowsdifferentuserapplicationprogramstoconcurrentlyaccessthesamedatabase.DBMSsmayuseavarietyofdatabasemodels,suchastherelationalmodelorobjectmodel,toconvenientlydescribeandsupportapplications.,Ittypicallysupportsquerylanguages,whichareinfacthigh-levelprogramminglanguages,dedicateddatabaselanguagesthatconsiderablysimplifywritingdatabaseapplicationprograms.Databaselanguagesalsosimplifythedatabaseorganizationaswellasretrievingandpresentinginformationfromit.ADBMSprovidesfacilitiesforcontrollingdataaccess,enforcingdataintegrity,managingconcurrencycontrol,andrecoveringthedatabaseafterfailuresandrestoringitfrombackupfiles,aswellasmaintainingdatabasesecurity.,9-1-3ApplicationCaseorExampleSQLServerMonitorMicrosoftSQLServerisarelationaldatabase-managementsystemthatscalesfromlaptopsanddesktopstoenterpriseservers,withacompatibleversion,basedontheWindowsMobileoperatingsystem,availableforhandhelddevicessuchasPocketPCs,SmartPhones,andPortableMediaCenters.,SQLServerprovidesasuiteoftoolsformanagingallaspectsofSQLServerdevelopment,querying,tuning,testing,andadministration.MostofthesetoolscenteraroundtheSQLServerManagementStudio.SQLServerManagementStudioprovidesacommonshellforadministeringallservicesassociatedwithSQLServer,whichincludesDatabaseEngine,AnalysisServices,ReportingServices,SQLServerMobile,andIntegrationServices.,SQL(StructuredQueryLanguage,referredtoassequelorbythelettersS-Q-L)isalanguagethatgivesusersaninterfacetoarelationaldatabasewheretheycanfindandprocessdatastoredwithin.Atthepresenttime,itisthemostwidelyuseddatabaselanguage.,Inthedatabase,informationisstoredintablesthataremadeupofmanycolumnsandrows.Eachcolumnhandlesaspecifictypeofinformation,andeachrowrepresentsarecordenteredintothetable.Arowmayrepresentacustomer,andeachcolumnmaycontainspecificsaboutthatcustomer.,MicrosoftSQLServerisapackagedbrandofSQLthatmanycompaniesuseanddependonfortheirdailyoperation.WhenacompanyinstallsSQLServer,itisusuallyusedforseveralpurposes,withtheserveradministratorcreatingadatabaseforeachuse.FormoreinformationaboutMicrosoftSQLServer,visitM:,AlongwiththefullversionofSQLServer,MicrosofthasalsodevelopedMSDE(MicrosoftDesktopEngine)whichworkslikeSQLserver,buthasa2GBlimitondata,andcontainsasingledatabase.ThereisalsoauserinterfacewithSQLServerthatisnotusedbyMSDE.,NomatterwhichversionofSQLServeryouuse,youshouldalwaysbeconcernedwithitsproperfunctionandconstantavailability.Withoutit,theinformationinthedatabasecannotberetrievedandmanyofyourapplicationsthatrelyonthedatabasewillsimplynotwork.UsinganetworkmonitoringtoollikeWhatsUpGoldPremiumEditionyoucankeepaconstantwatchoverspecificitemsorparametersinyourSQLserver.Thefollowingsectiondescribestheapplicationandhowyoucanuseittomonitoryourdatabases.,MonitoringSQLServerWhatsUpGoldStandardandPremiumEditionscanmonitorandreportthestatusofthestandardservicesassociatedwithstandardTCP/IPservers,suchasSMTP,POP3,andIMAP,FTP,HTTP.Ifanyoftheseservicesfail,youruserswillbeunabletogetmail,transferfiles,orusetheweb.Itisagoodideatosetupmonitoringontheseservicessothatyouarethefirsttoknowiftheyfail.,TheSQLServerMonitorextendsmonitoringtoparametersreportedbyMicrosoftSQLServer(andMicrosoftMSDE),allowingyoutogetanearlywarningofadegradationinperformance.Forexample,youcanmonitorsystemparametersonyourSQLServerdatabaseservertoseeifperformanceiswithinanexpectedrange,andifnot,youcanintervenebeforetheSQLServerfails.Inotherwords,youcandetectaloomingproblembeforeitcausesanapplicationorservicefailure.TheSQLServerMonitorsupportsmonitoringofMicrosoftSQLServer2000orlaterversions,andMSDE2000orlaterversions,whichcanbeonanymachineinyournetwork.,GettingStartedWiththeSQLMonitorBeforeconfigureuringyourSQLmonitor(s),youshoulddeterminewhichparametersandservicesyouneedtomonitor.Youshouldalsoconsiderwhetheryouwanttocreateasinglemonitorwithmultipleparameters,severalmonitorswithoneparameterorservice,oracombinationofthetwo.Ifyoucreateasinglemonitortowatchalloftheparameters,youwillnotknowwhichparameterhastheproblemuntilyoudoalittleresearch.Thereismoresetuptimewiththeotheroptions,butthetroubleshootingtimeisgreatlyreduced.,Note:Tousesomeoftheparameters,youmustconfigureyourSystemDataSource(ODB)namefortheSQLServer.ThisisdoneintheWindowsDataSources(ODB)Administrator.Duringthecreationofyourmonitors,youalsoassignthealertsandactionsyouwantWhatsUptofirewhenoneofthemonitorsgoesdown.,ConfiguringaSQLMonitorToconfigureaninstanceoftheSQLServerMonitor,youmustfirsthaveWhatsUpGoldPremiumEditioninstalled.Then:1.FromtheConfiguremenu,selectActiveMonitorLibrary.2.TheActiveMonitorLibraryisthestartingpointforcreatinganyActiveMonitorinWhatsUpGold.ThisdialogshowsalloftheActiveMonitorsinyourdatabase.,3.AddanSQLmonitor:ClickNew.TheSelectActiveMonitorTypedialogappears.SelectSQLServiceMonitorandclickOK.TheNewSQLServiceMonitor(SeeFigure9-1)dialogappears.,4.Selecttheparametersandorprocessestoaddtothemonitor.OncetheActiveMonitoriscreated,youcanassignthatmonitortothedevicerepresentingthecomputerrunningtheSQLServer.Youmayalsousethemonitorduringdevicediscovery.,Figure9-1NewSQLServerMonitor,AnExampleTomonitoruseractivity,wellcreateamonitorcalled“SQLUser,”thenselectUsersastheonlyparametertomonitor.1.AccesstheSQLServerMonitorpropertiesasdescribedinthesectionabove.2.Namethemonitor“SQLUser.”,3.MakesurethatUsersistheonlyparameterthathasacheckintheboxtothelefttoit.Youwillneedtocleartheselectionsfortheotherparametersandalsofortheprocesses.4.ClicktheUsersparametertoselectit,andthenclickConfigure.TheUsersThresholddialogappears.Youshouldhaveinmindhowmanyusersorconnectionsyouwanttoconsiderasathreshold,andenterthosevaluesintheappropriateboxesonthedialog.,5.Whenfinished,clickOKtoaddtheSQLUsermonitortotheActiveMonitorLibrary.Oncethemonitorhasbeencreated,youarereadytoaddthe“SQLUser”monitortoyourSQLserverdevice.1.SelectthedevicethatrepresentstheSQLserver.Double-clickthedevicetodisplayitsproperties.2.SelecttheActiveMonitorsicon.3.OntheActiveMonitordialog,clickAdd.TheActiveMonitorwizardappears.4.Followthewizardtoaddtheactivemonitortothedevice.,9-2ReadingMaterial9-2-1ReadingcomprehensionApplicationProgramsandUserInterfacesAlthoughmanypeopleinteractwithdatabases,veryfewpeopleuseaquerylanguagetointeractwithadatabasesystemdirectly.Themostcommonwayinwhichusersinteractwithdatabasesisthroughanapplicationprogramthatprovidesauserinterfaceatthefrontend,andinterfaceswithadatabaseatthebackend.,Suchapplicationstakeinputfromusers,typicallythroughaforms-basedinterface,andeitherenterdataintoadatabaseorextractinformationfromadatabasebasedontheuserinput,andgenerateoutput,whichisdisplayedtotheuser.,Asanexampleofanapplication,considerauniversityregistrationsystem.Likeothersuchapplications,theregistrationsystemfirstrequiresyoutoidentifyandauthenticateyourself,typicallybyausernameandpassword.Theapplicationthenusesyouridentitytoextractinformation,suchasyournameandthecoursesforwhichyouhaveregistered,fromthedatabaseanddisplaystheinformation.Theapplicationprovidesanumberofinterfacesthatletyouregisterforcoursesandqueryavarietyofotherinformationsuchascourseandinstructorinformation.Organizationsusesuchapplicationstoautomateavarietyoftasks,suchassales,purchases,accountingandpayroll,human-resourcesmanagement,andinventorymanagement,amongmanyothers.,Applicationprogramsmaybeusedevenwhenitisnotapparentthattheyarebeingused.Forexample,anewssitemayprovideapagethatistransparentlycustomizedtoindividualusers,eveniftheuserdoesnotexplicitlyfillanyformswheninteractingwiththesite.Todoso,itactuallyrunsanapplicationprogramthatgeneratesacustomizedpageforeachuser;customizationcan,forexample,bebasedonthehistoryofarticlesbrowsedbytheuser.,Atypicalapplicationprogramincludesafront-endcomponent,whichdealswiththeuserinterface,aback-endcomponent,whichcommunicateswithadatabase,andamiddlelayer,whichcontains“businesslogic,”thatis,codethatexecutesspecificrequestsforinformationorupdates,enforcingrulesofbusinesssuchaswhatactionsshouldbecarriedouttoexecuteagiventask,orwhocancarryoutwhattask.,Applicationarchitectureshaveevolvedovertime,asillustratedinFigure9-2.Applicationssuchasairlinereservationshavebeenaroundsincethe1960s.Intheearlydaysofcomputerapplications,applicationsranonalarge“mainframe”computer,andusersinteractedwiththeapplicationthroughterminals,someofwhichevensupportedforms.,Figure9-2Applicationarchitecturesindifferenteras,Withthewidespreaduseofpersonalcomputers,manyorganizationsusedadifferentarchitectureforinternalapplications,withapplicationsrunningontheuserscomputer,andaccessingacentraldatabase.Thisarchitecture,oftencalleda“clientserver”architecture,allowedthecreationofpowerfulgraphicaluserinterfaces,whichearlierterminal-basedapplicationsdidnotsupport.,Inthepast15years,Webbrowsershavebecometheuniversalfrontendtodatabaseapplications,connectingtothebackendthroughtheInternet.Browsersuseastandardizedsyntax,theHyperTextMarkupLanguage(HTML)standard,whichsupportsbothformatteddisplayofinformation,andcreationofforms-basedinterfaces.The