小区物业综合管理系统的设计与实现外文翻译.docx

小区物业综合管理系统的设计与实现外文翻译.docx

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小区物业综合管理系统的设计与实现外文翻译

（学校名字）

本科毕业设计（外文翻译）

题目小区物业综合管理系统的设计与实现

学生姓名

专业班级

学号

院（系）

指导教师（职称）

完成时间

Databasespaceorganization

Spatialdatamanagementhasbeenanactiveareaofresearchinthedatabasefieldfortwodecades，withmuchoftheresearchbeingfocusedondevelop-ingdatastructuresforstoringandindexingspatialdata.However,nocommercialdatabasesystempro-videsfacilitiesfordirectlydefiningandstoringspa-tialdata,andforniulatingqueriesbasedonresearchconditionsonspatialdata.Webelievethefollowingaretherelevantissuesonwhichnear-termresearchshouldbefocused（intheorderofdecreasingimpor-tanceandurgency）．  

　　First,relationalqueryoptimizationtechniquesneedtobeextendedtodealwithspatialqueries，thatis，queriesthatcontainsearchconditionsonspatialpredicatestobedeveloped.   

　　Second,moreworkneedstobedoneonexperi-mentalvalidationoftherelativeperformanceofsomeofthemorepromisingdatastructuresandindexingstructuresproposedthusfar,withconsiderationofamuchbroadersetofoperationsthanjustafewopera-tionsthathavetypicallybeenusedinthelimitedper-formancestudiesconductedthusfar.   

　　Third,itisdifficulttobuildintoasingledata-basesystemmultipledatastructuresforspatialindex-ing,andallspatialoperatorsthatareusefulforawidevarietyofspatialapplications，assuch,itisdesirabletobuildadatabasesystemsothatitwillbeaseasyaspossibletoextendthesystemwithaddi-tionaldatastructuresandspatialoperators．

IftheDBMSprovidesawaytointeractivelyandupdatethedatabase,aswellasinterrogateitcapabilityallowsformanagingpersonaldata-Aceshowever,itdoesnotautomaticallyleaveanaudittrailofactionsanddoesnotprovidethekindsofcontrolanecessaryinamultiuserorganization.These-controlsareonlyavailablewhenasetofapplicationprogramsarecustomizedforeachdataentryandupdatingfunction.   

　　SoftwareforpersonalcomputerswhichperformmeoftheDBMSfunctionshavebeenverypopular  arsenalcomputerswereintendedforusebyindividualsforpersonalinformationstorageandprocess-Thesemachineshavealsobeenusedextensivelysmallenterprises,professionalslikedoctors,acrylics,engineers,lawyersandsoon．Bythenatureof.intendedusage,databasesystemsonthesemachinesexceptfromseveraloftherequirementsoffulldogedatabasesystems．Sincedatasharingisnot：

Tended,concurrentoperationsevenlessso,the）fewercanbelesscomplex.Securityandintegrity7aintenancearede-emphasizedorabsent.Asdata-）limeswillbesmall,performanceefficiencyIsalsoimportant.Infact,theonlyaspectofadatabasesystemthatisImportant'isdataIndependence.Data-.dependence,asstatedearlier.Meansthatapplicantprogramsanduserqueriesneednotrecognizant‘physicalorganizationofdataonsecondarystorage.Theimportanceofthisaspect,particularlyforthepersonalcomputeruser,isthatthisgreatlysimplifiesdatabaseusage.Theusercanstore,accessandmanipulatedataatahighlevel（closetotheapplication）andbetotallyshieldedfromthelowlevel（closetothemachine）detailsofdataorganization.WewillnotdiscussdetailsofspecificPCDBMSsoftwarepackageshere．Letussummarizeinthefollowingthestrengthsandweaknessesofpersonalcomputerdata-basesoftwaresystems：

　　Themostobviouspositivefactoristheuserfriendlinessofthesoftware.Auserwithnopriorcomputerbackgroundwouldbeabletousethesystemtostorepersonalandprofessionaldata,retrieveandperformrelayedprocessing.Theusershould,ofcourse,satietyhimselfaboutthequalityofsoftwareandthefreedomfromerrors（bugs）sothatinvest-meritsindataarcprotected.   

　　Fortheprogrammerimplementingapplicationswiththem,theadvantageliesinthesupportforapplicationsdevelopmentintermsofinputscreengenerations,outputreportgenerationetc．offeredbythesesstems．   

　　Themainnegativepointconcernsabsenceofdataprotectionfeatures．Unlessencrypted,datacaneaccessedbywhoeverhasaccesstothemachineDatacanbedestroyedthroughmistakesormaliciousintent.ThesecondweaknessofmanvofthePC-basedsystemsisthatofperformance.Ifdatavolumesgrowuptoafewthousandsofrecords，performancecouldbeabottleneck．

　　Fororganizationwheregrowthindatavolumesisexpected,availabilityof,thesameorcompatiblesoftwareonlargemachinesshouldbeconsidered. 

Thisisoneofthemostcommonmisconceptionsaboutdatabasemanagementsystemsthatareusedinpersonalcomputers．ThoroughlycomprehensiveandsophisticatedbusinesssystemscanbedevelopedindBASh,ParadoxandotherDBMSs．However,theyarecreatedbyexperiencedprogrammersusingtheDBMS'sownprogramminglanguage.Thatisnotthesameasuserswhocreateandmanagepersonalfilesthatarenotpartofthemainstreamcompanysystem．

Datasecuritypreventsunauthorizedusersfromviewingorupdatingthedatabase．Usingpasswords,the  database,  called  subschema（pronounced"sub-scheme"），Forexample,anemployeedatabasecancontainallthedataaboutanindividualemployee,butonegroupofusersmaybeauthorizedtoviewonlypayrolldata,whileothersareallowedaccesstoonlyworkhistoryandmedicaldata.   

　　TheDBMScanmaintaintheintegrityofthedatabasebynotallowingmorethanoneusertoup-datethesamerecordatthesametime,TheDBMScankeepduplicaterecordsoutofthedatabase,forexample,notwocustomerswiththesamecustomernumbers（Keyfields）canbeenteredintotheData-Base.   

　　WhenaDBMSisused,thedetailedknowledgeofthephysicalorganizationofthedatadoesnothavetobebuiltintoeveryapplicationprogram.TheapplicationprogramaskstheDBMSfordatabyfieldpine,forexample,Icodedrepresentationof"give customernameandbalancedue"wouldbesenttoheDBMS．WithoutaDBMS,theprogrammermustsecrecyspaceforthefullstructureoftheintheprogram,Anychangeindatastructurerequires￡hangsinalltheapplicationsprograms．

Themultiple-databasemodelisrepresentedbyproposalsforsharedandprivatedatabasearchitectrues,checkoutandcheckingofdatatoandfromsharedandprivatedatabases．Eachusermaypopulates/herprivatedatabasewithdatacheckedoutoftheshareddatabase,performupdatesagainstthedata.andcheckthembackintothesharedDatabase.   

　　Themultiple-databasemodelcanbeusedto workaround"theconflictsituationsinherentinlonglunationdatabasesessions．Sinceeachuserfromtheshareddatabaseandworkagainst.is/herprivatedatabase,"disconnected"fromthe、hareddatabase（atleastonthesurface），theusersanavoidtheconflictsituations．Inparticular,multileusersmaybesimultaneouslyupdatingthesamethoughthavingtowaitforotheruserstocomatelatetheirupdates．However,whenupdatedistobeneckedintotheshareddatabase,itmayhavetobecheckedinasanewversion,necessitatingversionmanagement.Further,'whendatainaprivatedata-basereferencesdataintheshareddata，orviceversa,aprivatedatabaseisnotreallydisconnectedfromtheshareddatabase.Forexample,theevaluationofqueryingeneralwillrequirethedatabasesystemtoaccessbothaprivatedatabaseandtheshareddata-base,evenifthequerymayhavebeenformulatedagainstaprivatedatabase．Themultiple-databasemodelismoreappropriatethanthesingle-databasemodelinanenvironmentwhereitiseasytodetermineinadvancelogicalpartitionsofthedatabasethatcorrespondtoworktobeperformed.

Thesingle-databasemodelhasreceivedconsiderablymoreattentionthanthemultiple-databasemodel．Thefocusofresearchintosingle-databasemodelhasbeenonaddressingthetwinproblemoflongwaitsandlossofworkthatthelongdurationoftransactionsbringsabout.   

　　Thesingle-databasemodelrequirestheintro-dictionofanotionofdatabaseconsistency,andprotocolsforconcurrencycontrolandrecovery,thataredifferentfromthosesupportedintraditionaldatabasesystems．Ifa"reasonable"notionofdatabaseconsistencyistobesupported（I．c.thedatabasesystemistoenforceitautomatically）,thereareboundtobe”conflict"situationswhereonetransactioncomesintoanaccessconflictagainstsomeothertransaction.Ifawaitistobeavoided，somemeansofanegotiatedsettlementoftheconflictmustbeprovided,therebydraggingtheusersintothedetailsofconcurrencycontrol．Thesingle-databasemodelismoreappropriate-atethanthemultiple-databasemodelinanenvironmentwhereitisdifficulttodetermineinadvancelogicalpartitionsofthedatabasethatcorrespondtoworktobeperformed,andtheuserscloselycooperate.

Theobjectiveoflong-durationtransactionsistomodellong-duration,interactiveDatabaseaccesssessionsinapplicationenvironments．Thefundamentalassumptionaboutshort-durationoftransactionsthatunderliesthetraditionalmodeloftransactionsisinappropriateforlong-durationtransactions．Theimplementationofthetraditionalmodeloftransactionsmaycauseintolerablylongwaitswhentransactionsalephtoacquirelocksbeforeaccessingdata,andmayalsocausealargeamountofworktobelostwhentransactionsarebackedoutinresponsetouser-initiatedabortsorsystemfailuresituations．   

　　Theobjectiveofatransactionmodelistopro-videarigorousbasisforautomaticallyenforcingcriterionfordatabaseconsistencyforasetofmultipleconcurrentreadandwriteaccessestothedatabaseinthepresenceofpotentialsystemfailuresituations．Theconsistencycriterionadoptedfortraditionaltransactionsisthenotionofscrializability．Scrializa-bilityisenforcedinconventionaldatabasesystemsthroughtheu