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外文资料原文DATABASESYSTEMS1INTRODUCTIONTODATABASESYSTEMTODAY,MORETHANATANYPREVIOUSTIME,THESUCCESSOFANORGANIZATIONDEPENDSONITSABILITYTOACQUIREACCURATEANDTIMELYDATAABOUTITSOPERATION,TOMANAGETHISDATAEFFECTIVELY,ANDTOUSEITTOANALYZEANDGUIDEITSACTIVITIESPHRASESSUCHASTHEINFORMATIONSUPERHIGHWAYHAVEBECOMEUBIQUITOUS,ANDINFORMATIONPROCESSINGISARAPIDLYGROWINGMULTIBILLIONDOLLARINDUSTRYTHEAMOUNTOFINFORMATIONAVAILABLETOUSISLITERALLYEXPLODING,ANDTHEVALUEOFDATAASANORGANIZATIONALASSETISBEINGWIDELYRECOGNIZEDTHISPARADOXDRIVESTHENEEDFORINCREASINGLYPOWERFULANDFLEXIBLEDATAMANAGEMENTSYSTEMSADATABASEISACOLLECTIONOFDATA,TYPICALLYDESCRIBINGTHEACTIVITIESOFONEORMORERELATEDORGANIZATIONSFOREXAMPLE,AUNIVERSITYDATABASEMIGHTCONTAININFORMATIONABOUTTHEFOLLOWINGENTITIESSUCHASSTUDENTS,FACULTY,COURSES,ANDCLASSROOMSRELATIONSHIPSBETWEENENTITIES,SUCHASSTUDENTSENROLLMENTINCOURSES,FACULTYTEACHINGCOURSES,ANDTHEUSEOFROOMSFORCOURSESADATABASEMANAGEMENTSYSTEM,ORDBMS,ISSOFTWAREDESIGNEDTOASSISTINMAINTAININGANDUTILIZINGLARGECOLLECTIONSOFDATA,ANDTHENEEDFORSUCHSYSTEMS,ASWELLASTHEIRUSE,ISGROWINGRAPIDLYTHEALTERNATIVETOUSINGADBMSISTOUSEADHOCAPPROACHESTHATDONOTCARRYOVERFROMONEAPPLICATIONTOANOTHER,FOREXAMPLE,TOSTORETHEDATAINFILESANDWRITEAPPLICATIONSPECIFICCODETOMANAGEITTHEAREAOFDATABASEMANAGEMENTSYSTEMSISAMICROCOSMOFCOMPUTERSCIENCEINGENERALTHEISSUESADDRESSEDANDTHETECHNIQUESUSEDSPANAWIDESPECTRUM,INCLUDINGLANGUAGES,OBJECTORIENTATIONANDOTHERPROGRAMMINGPARADIGMS,COMPILATION,OPERATINGSYSTEMSCONCURRENTPROGRAMMING,DATASTRUCTURES,ALGORITHMS,THEORY,PARALLELANDDISTRIBUTEDSYSTEMS,USERINTERFACES,EXPERTSYSTEMSANDARTIFICIALINTELLIGENCE,STATISTICALTECHNIQUES,ANDDYNAMICPROGRAMMINGDATABASEMANAGEMENTCONTINUESTOGAINIMPORTANCEASMOREANDMOREDATAISBROUGHTONLINE,ANDMADEEVERMOREACCESSIBLETHROUGHCOMPUTERNETWORKINGTODAYTHEFIELDISBEINGDRIVENBYEXCITINGVISIONSSUCHASMULTIMEDIADATABASES,INTERACTIVEVIDEO,DIGITALLIBRARIES,AHOSTOFSCIENTIFICPROJECTSSUCHASTHEHUMANGENOMEMAPPINGEFFORTANDNASASEARTHOBSERVATIONSYSTEMPROJECT,ANDTHEDESIREOFCOMPANIESTOCONSOLIDATETHEIRDECISIONMAKINGPROCESSESANDMINETHEIRDATAREPOSITORIESFORUSEFULINFORMATIONABOUTTHEIRBUSINESSCOMMERCIALLY,DATABASEMANAGEMENTSYSTEMSREPRESENTONEOFTHELARGESTANDMOSTVIGOROUSMARKETSEGMENTSTHUSTHESTUDYOFDATABASESYSTEMSCOULDPROVETOBERICHLYREWARDINGINMOREWAYSTHANONE2DATABASECONSISTSADATABASECONSISTSOFAFILEORASETOFFILESTHEINFORMATIONINTHESEFILESMAYBEBROKENDOWNINTORECORDS,EACHOFWHICHCONSISTSOFONEORMOREFIELDSFIELDSARETHEBASICUNITSOFDATASTORAGE,ANDEACHFIELDTYPICALLYCONTAINSINFORMATIONPERTAININGTOONEASPECTORATTRIBUTEOFTHEENTITYDESCRIBEDBYTHEDATABASEUSINGKEYWORDSANDVARIOUSSORTINGCOMMANDS,USERSCANRAPIDLYSEARCH,REARRANGE,GROUP,ANDSELECTTHEFIELDSINMANYRECORDSTORETRIEVEORCREATEREPORTSONPARTICULARAGGREGATESOFDATADATABASERECORDSANDFILESMUSTBEORGANIZEDTOALLOWRETRIEVALOFTHEINFORMATIONEARLYSYSTEMSWEREARRANGEDSEQUENTIALLYIE,ALPHABETICALLY,NUMERICALLY,ORCHRONOLOGICALLYTHEDEVELOPMENTOFDIRECTACCESSSTORAGEDEVICESMADEPOSSIBLERANDOMACCESSTODATAVIAINDEXESQUERIESARETHEMAINWAYUSERSRETRIEVEDATABASEINFORMATIONTYPICALLY,THEUSERPROVIDESASTRINGOFCHARACTERS,ANDTHECOMPUTERSEARCHESTHEDATABASEFORACORRESPONDINGSEQUENCEANDPROVIDESTHESOURCEMATERIALSINWHICHTHOSECHARACTERSAPPEARAUSERCANREQUEST,FOREXAMPLE,ALLRECORDSINWHICHTHECONTENTOFTHEFIELDFORAPERSONSLASTNAMEISTHEWORDSMITHINFLATDATABASES,RECORDSAREORGANIZEDACCORDINGTOASIMPLELISTOFENTITIESMANYSIMPLEDATABASESFORPERSONALCOMPUTERSAREFLATINSTRUCTURETHERECORDSINHIERARCHICALDATABASESAREORGANIZEDINATREELIKESTRUCTURE,WITHEACHLEVELOFRECORDSBRANCHINGOFFINTOASETOFSMALLERCATEGORIESUNLIKEHIERARCHICALDATABASES,WHICHPROVIDESINGLELINKSBETWEENSETSOFRECORDSATDIFFERENTLEVELS,NETWORKDATABASESCREATEMULTIPLELINKAGESBETWEENSETSBYPLACINGLINKS,ORPOINTERS,TOONESETOFRECORDSINANOTHERTHESPEEDANDVERSATILITYOFNETWORKDATABASESHAVELEDTOTHEIRWIDEUSEINBUSINESSRELATIONALDATABASESAREUSEDWHEREASSOCIATIONSAMONGFILESORRECORDSCANNOTBEEXPRESSEDBYLINKSASIMPLEFLATLISTBECOMESONETABLE,OR“RELATION”,ANDMULTIPLERELATIONSCANBEMATHEMATICALLYASSOCIATEDTOYIELDDESIREDINFORMATIONOBJECTORIENTEDDATABASESSTOREANDMANIPULATEMORECOMPLEXDATASTRUCTURES,CALLED“OBJECTS”,WHICHAREORGANIZEDINTOHIERARCHICALCLASSESTHATMAYINHERITPROPERTIESFROMCLASSESHIGHERINTHECHAINTHISDATABASESTRUCTUREISTHEMOSTFLEXIBLEANDADAPTABLE3STRUCTUREOFTHERELATIONALDATABASETHERELATIONALMODELISTHEBASISFORANYRELATIONALDATABASEMANAGEMENTSYSTEMRDBMSARELATIONALMODELHASTHREECORECOMPONENTSACOLLECTIONOFOBJECTSORRELATIONS,OPERATORSTHATACTONTHEOBJECTSORRELATIONS,ANDDATAINTEGRITYMETHODSINOTHERWORDS,ITHASAPLACETOSTORETHEDATA,AWAYTOCREATEANDRETRIEVETHEDATA,ANDAWAYTOMAKESURETHATTHEDATAISLOGICALLYCONSISTENTARELATIONALDATABASEUSESRELATIONS,ORTWODIMENSIONALTABLES,TOSTORETHEINFORMATIONNEEDEDTOSUPPORTABUSINESS31TABLES,ROW,ANDCOLUMNSATABLEINARELATIONALDATABASE,ALTERNATIVELYKNOWNASARELATION,ISATWODIMENSIONALSTRUCTUREUSEDTOHOLDRELATEDINFORMATIONADATABASECONSISTSOFONEORMORERELATEDTABLESNOTEDONTCONFUSEARELATIONWITHRELATIONSHIPSARELATIONISESSENTIALLYATABLE,ANDARELATIONSHIPISAWAYTOCORRELATE,JOIN,ORASSOCIATETWOTABLESAROWINATABLEISACOLLECTIONORINSTANCEOFONETHING,SUCHASONEEMPLOYEEORONELINEITEMONANINVOICEACOLUMNCONTAINSALLTHEINFORMATIONOFASINGLETYPE,ANDTHEPIECEOFDATAATTHEINTERSECTIONOFAROWANDACOLUMN,AFIELD,ISTHESMALLESTPIECEOFINFORMATIONTHATCANBERETRIEVEDWITHTHEDATABASESQUERYLANGUAGEFOREXAMPLE,ATABLEWITHINFORMATIONABOUTEMPLOYEESMIGHTHAVEACOLUMNCALLEDLAST_NAMETHATCONTAINSALLOFTHEEMPLOYEESLASTNAMESDATAISRETRIEVEDFROMATABLEBYFILTERINGONBOTHTHEROWANDTHECOLUMN32PRIMARYKEYS,DATATYPES,ANDFOREIGNKEYSRELATIONATWODIMENSIONALSTRUCTUREUSEDTOHOLDRELATEDINFORMATION,ALSOKNOWNASATABLEROWAGROUPOFONEORMOREDATAELEMENTSINADATABASETABLETHATDESCRIBESAPERSON,PLACE,ORTHINGCOLUMNTHECOMPONENTOFADATABASETABLETHATCONTAINSALLOFTHEDATAOFTHESAMENAMEANDTYPEACROSSALLROWSPRIMARYKEYACOLUMNORCOLUMNSINATABLETHATMAKESTHEROWINTHETABLEDISTINGUISHABLEFROMEVERYOTHERROWINTHESAMETABLEDATATYPESNUMERICVALUES,CHARACTERORALPHABETICVALUES,ANDDATEVALUESAFOREIGNKEYENFORCESTHECONCEPTOFREFERENTIALINTEGRITYINARELATIONALDATABASEFOREIGNKEYACOLUMNORCOLUMNSINATABLETHATDRAWSITSVALUESFROMAPRIMARYORUNIQUEKEYCOLUMNINANOTHERTABLEAFOREIGNKEYASSISTSINENSURINGTHEDATAINTEGRITYOFATABLEREFERENTIALINTEGRITYAMETHODEMPLOYEDBYARELATIONALDATABASESYSTEMTHATENFORCESONETOMANYRELATIONSHIPSBETWEENTABLES33DATAMODELINGINTHISPROCESS,THEDEVELOPERCONCEPTUALIZESANDDOCUMENTSALLTHETABLESFORTHEDATABASEONEOFTHECOMMONMETHODSFORMODELINGADATABASEISCALLEDERA,WHICHSTANDSFORENTITIES,RELATIONSHIPS,ANDATTRIBUTESTHEDATABASEDESIGNERUSESANAPPLICATIONTHATCANMAINTAINENTITIES,THEIRATTRIBUTES,ANDTHEIRRELATIONSHIPSINGENERAL,ANENTITYCORRESPONDSTOATABLEINTHEDATABASE,ANDTHEATTRIBUTESOFTHEENTITYCORRESPONDTOCOLUMNSOFTHETABLEDATAMODELINGAPROCESSOFDEFININGTHEENTITIES,ATTRIBUTES,ANDRELATIONSHIPSBETWEENTHEENTITIESINPREPARATIONFORCREATINGTHEPHYSICALDATABASETHEDATAMODELINGPROCESSINVOLVESDEFININGTHEENTITIES,DEFININGTHERELATIONSHIPSBETWEENTHOSEENTITIES,ANDTHENDEFININGTHEATTRIBUTESFOREACHOFTHEENTITIESONCEACYCLEISCOMPLETE,ITISREPEATEDASMANYTIMESASNECESSARYTOENSURETHATTHEDESIGNERISCAPTURINGWHATISIMPORTANTENOUGHTOGOINTOTHEDATABASELETSTAKEACLOSERLOOKATEACHSTEPINTHEDATAMODELINGPROCESS34DEFININGTHEENTITIESFIRST,THEDESIGNERIDENTIFIESALLOFTHEENTITIESWITHINTHESCOPEOFTHEDATABASEAPPLICATIONTHEENTITIESARETHEPERSONS,PLACES,ORTHINGSTHATAREIMPORTANTTOTHEORGANIZATIONANDNEEDTOBETRACKEDINTHEDATABASEENTITIESWILLMOSTLIKELYTRANSLATENEATLYTODATABASETABLES35DEFININGTHERELATIONSHIPSBETWEENENTITIESONCETHEENTITIESAREDEFINED,THEDESIGNERCANPROCEEDWITHDEFININGHOWEACHOFTHEENTITIESISRELATEDOFTEN,THEDESIGNERWILLPAIREACHENTITYWITHEVERYOTHERENTITYANDASK,“ISTHEREARELATIONSHIPBETWEENTHESETWOENTITIES“SOMERELATIONSHIPSAREOBVIOUSSOMEARENOTINTHEWIDGETCOMPANYDATABASE,THEREISMOSTLIKELYARELATIONSHIPBETWEENEMPANDDEPT,BUTDEPENDINGONTHEBUSINESSRULES,ITISUNLIKELYTHATTHEDEPTANDSALGRADEENTITIESARERELATEDIFTHEBUSINESSRULESWERETORESTRICTCERTAINSALARYGRADESTOCERTAINDEPARTMENTS,THEREWOULDMOSTLIKELYBEANEWENTITYTHATDEFINESTHERELATIONSHIPBETWEENSALARYGRADESANDDEPARTMENTSTHISENTITYWOULDBEKNOWNASANASSOCIATIVEORINTERSECTIONTABLEANDWOULDCONTAINTHEVALIDCOMBINATIONSOFSALARYGRADESANDDEPARTMENTSASSOCIATIVETABLEADATABASETABLETHATSTORESTHEVALIDCOMBINATIONSOFROWSFROMTWOOTHERTABLESANDUSUALLYENFORCESABUSINESSRULEANASSOCIATIVETABLERESOLVESAMANYTOMANYRELATIONSHIPINGENERAL,THEREARETHREETYPESOFRELATIONSHIPSINARELATIONALDATABASEONETOMANYTHEMOSTCOMMONTYPEOFRELATIONSHIPISONETOMANYTHISMEANSTHATFOREACHOCCURRENCEINAGIVENENTITY,THEPARENTENTITY,THEREMAYBEONEORMOREOCCURRENCESINASECONDENTITY,THECHILDENTITY,TOWHICHITISRELATEDFOREXAMPLE,INTHEWIDGETCOMPANYDATABASE,THEDEPTENTITYISAPARENTENTITY,ANDFOREACHDEPARTMENT,THERECOULDBEONEORMOREEMPLOYEESASSOCIATEDWITHTHATDEPARTMENTTHERELATIONSHIPBETWEENDEPTANDEMPISONETOMANYONETOONEINAONETOONERELATIONSHIP,AROWINATABLEISRELATEDTOONLYONEORNONEOFTHEROWSINASECONDTABLETHISRELATIONSHIPTYPEISOFTENUSEDFORSUBTYPINGFOREXAMPLE,ANEMPLOYEETABLEMAYHOLDTHEINFORMATIONCOMMONTOALLEMPLOYEES,WHILETHEFULLTIME,PARTTIME,ANDCONTRACTORTABLESHOLDINFORMATIONUNIQUETOFULLTIMEEMPLOYEES,PARTTIMEEMPLOYEES,ANDCONTRACTORS,RESPECTIVELYTHESEENTITIESWOULDBECONSIDEREDSUBTYPESOFANEMPLOYEEANDMAINTAINAONETOONERELATIONSHIPWITHTHEEMPLOYEETABLETHESERELATIONSHIPSARENOTASCOMMONASONETOMANYRELATIONSHIPS,BECAUSEIFONEENTITYHASANOCCURRENCEFORACORRESPONDINGROWINANOTHERENTITY,INMOSTCASES,THEATTRIBUTESFROMBOTHENTITIESSHOULDBEINASINGLEENTITYMANYTOMANYINAMANYTOMANYRELATIONSHIP,ONEROWOFATABLEMAYBERELATEDTOMANYROWSOFANOTHERTABLE,ANDVICEVERSAUSUALLY,WHENTHISRELATIONSHIPISIMPLEMENTEDINTHEDATABASE,ATHIRDENTITYISDEFINEDASANINTERSECTIONTABLETOCONTAINTHEASSOCIATIONSBETWEENTHETWOENTITIESINTHERELATIONSHIPFOREXAMPLE,INADATABASEUSEDFORSCHOOLCLASSENROLLMENT,THESTUDENTTABLEHASAMANYTOMANYRELATIONSHIPWITHTHECLASSTABLEONESTUDENTMAYTAKEONEORMORECLASSES,ANDAGIVENCLASSMAYHAVEONEORMORESTUDENTSTHEINTERSECTIONTABLESTUDENT_CLASSWOULDCONTAINTHECOMBINATIONSOFSTUDENTANDCLASSTOTRACKWHICHSTUDENTSAREINWHICHCLASSES4DBMSINTRODUCTIONTHETERMDATABASEISOFTENTODESCRIBEACOLLECTONOFRELATEDFILESTHATISORGANIZEDINTOANINTE7ATEDSTRUCTURETHATPROVIDESDIFFERENTPEOPLEVARIANCESTOTHESAMEDATAFOREXAMPLE,THEDEPARTMENTMOTORVEHICLESHASADATABASEOFALLTHEINFORMALONDRIVERSLICENSESINALLCOUNTIESANDCITIESINSTATESOMEOFTHEINFORMATIONINTHEFILESEGPASTCRIMINALRECORD,CONVICTIONS，ANDTHELIKEMAYBEMADEAVAILABLETOPOLICEDEPARTMENTS,OTHERINFORMATIONEGABALANCEDUEONASPEEDINGTICKETMAYBEMADEAVAILABLETOLICENSINGBUREAUS,ANDSTILLOTHERINFORMATIONEGNUMBERANDTYPEOFCONVICTIONSMAYGOTOINSURANCECOMPANIESADATABASEMANAGEMENTSYSTEMDBMSISANEXTREMELYCOMPLICATEDSETOFSOFTWAREPROGRAMSTHATCONTROLSTHEORGANIZATION,STORAGEANDRETRIEVALOFDATAFELIDS,RECORDSANDFILESINADATABASEITALSOCONTROLSTHESECURITYANDINTEGRITYOFTHEDATABASESTHEDBMSACCEPTSREQUESTSFORDATAFROMTHEAPPLICATIONPROGRAMANDINSTRUCTSTHEOPERATINGSYSTEMTOTRANSFERTHEAPPROPRIATEDATATASKSTHATWOULDBETIMECONSUMINGTOACCOMPLISHMANUALLYAREMOREPRACTICALTHEAIDOFTHECOMPUTERINPRINCIPLE,ADATABASEINACOMPUTERISNOTDIFFERENTFROMADATABASERECORDEDONPAPERANDFILEDINCABINETSBUTTHECOMPUTERDOESTHETEDIOUSWORKOFMAINTAININGANDACCESSINGADATABASE,ANDDOESITFASTACOMPUTERIZEDDATABASETHATCANDOALLTHISISKNOWNASADATABASEMANAGEMENTSYSTEM,ORDBMSFORSHORTTHEREAREANUMBEROFWAYSTOSTOREINFORMATIONINACOMPUTER,BUTNOTALLOFTHESEARETRUEDATABASEMANAGEMENTSYSTEMSWHENADBMSISUSED,INFORMATIONSYSTEMSCANBECHANGEDMUCHMOREEASILYASTHEORGANIZATIONSINFORMATIONREQUIREMENTSCHANGENEWCATEGORIESOFDATACANBEADDEDTOTHEDATABASEWITHOUTDISRUPTIONTOTHEEXISTINGSYSTEM41DBMSDATABASEMANAGEMENTSYSTEMDBMSISABLETOACCESSANDRETRIEVEDATAFROMNONKEYRECORDFIELDSTHATIS,THEDBMSISABLETOSTRUCTUREANDTIETOGETHERTHELOGICALLYRELATEDDATAFROMSEVERALLARGEFILES42LOGICALSTRUCTURESIDENTIFYINGTHESELOGICALRELATIONSHIPSISAJOBOFTHEDATAADMINISTRATORADATADEFINITIONLANGUAGEISUSEDFORTHISPURPOSETHEDBMSMAYTHENEMPLOYONEOFTHEFOLLOWINGLOGICALSTRUCTURINGTECHNIQUESDURINGSTORAGEACCESS,ANDRETRIEVALOPERATIONS1LISTSTRUCTURESINTHISLOGICALAPPROACH,RECORDSARELINKEDTOGETHERBYTHEUSEOFPOINTERSAPOINTERISADATAITEMINONERECORDTHATIDENTIFIESTHESTORAGELOCATIONOFANOTHERLOGICALLYRELATEDRECORDRECORDSINACUSTOMERMASTERFILE,FOREXAMPLE,WILLCONTAINTHENAMEANDADDRESSOFEACHCUSTOMERANDEACHRECORDINTHISFILEISIDENTIFIEDBYANACCOUNTNUMBERDURINGANACCOUNTINGPERIOD,ACUSTOMERMAYBUYANUMBEROFITEMSONDIFFERENTDAYSTHUS,THECOMPANYMAYMAINTAINANINVOICEFILETOREFLECTTHESETRANSACTIONSALISTSTRUCTURECOULDBEUSEDINTHISSITUATIONTOSHOWTHEUNPAIDINVOICESATANYGIVENTIMEEACHRECORDINTHECUSTOMERFILEWOULDCONTAINAFIELDTHATWOULDPOINTTOTHERECORDLOCATIONOFTHEFIRSTINVOICEFORTHATCUSTOMERINTHEINVOICEFILETHISINVOICERECORD,INTURN,WOULDBELINKEDTOLATERINVOICESFORTHECUSTOMERTHELASTINVOICEINTHECHAINWOULDBEIDENTIFIEDBYTHEUSEOFASPECIALCHARACTERASAPOINTER2HIERARCHICALTREESTRUCTURESINTHISLOGICALAPPROACH,DATAUNITSARESTRUCTUREDINMULTIPLELEVELSTHATGRAPHICALLYRESEMBLEAN“UPSIDEDOWN“TREEWITHTHEROOTATTHETOPANDTHEBRANCHESFORMEDBELOWTHERESASUPERIORSUBORDINATERELATIONSHIPINAHIERARCHICALTREESTRUCTUREBELOWTHESINGLEROOTDATACOMPONENTARESUBORDINATEELEMENTSORNODES,EACHOFWHICH,INTURN,“OWN“ONEORMOREOTHERELEMENTSORNONEEACHELEMENTORBRANCHINTHISSTRUCTUREBELOWTHEROOTHASONLYASINGLEOWNERTHUS,ACUSTOMEROWNSANINVOICE,ANDTHEINVOICEHASSUBORDINATEITEMSTHEBRANCHESINATREESTRUCTUREARENOTCONNECTED3NETWORKSTRUCTURESUNLIKETHETREEAPPROACH,WHICHDOESNOTPERMITTHECONNECTIONOFBRANCHES,THENETWORKSTRUCTUREPERMITSTHECONNECTIONOFTHENODESINAMULTIDIRECTIONALMANNERTHUS,EACHNODEMAYHAVESEVERALOWNERSANDMAY,INTURN,OWNANYNUMBEROFOTHERDATAUNITSDATAMANAGEMENTSOFTWAREPERMITSTHEEXTRACTIONOFTHENEEDEDINFORMATIONFROMSUCHASTRUCTUREBYBEGINNINGWITHANYRECORDINAFILEDATABASEMANAGEMENTSYSTEMS（DBMS）ANDMANAGEMENTINFORMATIONSYSTEMS（MIS）YOUKNOWTHATADATABASEISACOLLECTIONOFLOGICALLYRELATEDDATAELEMENTSTHATMAYBESTRUCTUREDINVARIOUSWAYSTOMEETTHEMULTIPLEPROCESSINGANDRETRIEVALNEEDSOFORGANIZATIONSANDINDIVIDUALSTHERESNOTHINGNEWABOUTDATABASESEARLYONESWERECHISELEDINSTONE，PENNEDONSCROLLS，ANDWRITTENONINDEXCARDSBUTNOWDATABASESARECOMMONLYRECORDEDONMAGNETIZABLEMEDIA，ANDCOMPUTERPROGRAMSAREREQUIREDTOPERFORMTHENECESSARYSTORAGEANDRETRIEVALOPERATIONSYOULLSEEINTHEFOLLOWINGPAGESTHATCOMPLEXDATARELATIONSHIPSANDLINKAGESMAYBEFOUNDINALLBUTTHESIMPLESTDATABASESTHESYSTEMSOFTWAREPACKAGETHATHANDLESTHEDIFFICULTTASKSASSOCIATEDWITHCREATING，ACCESSING，ANDMAINTAININGDATABASERECORDSISCALLEDADATABASEMANAGEMENTSYSTEM（DBMS）THEPROGRAMSINADBMSPACKAGEESTABLISHANINTERFACEBETWEENTHEDATABASEITSELFANDTHEUSERSOFTHEDATABASE（THESEUSERSMAYBEAPPLICATIONSPROGRAMMERS，MANAGERSANDOTHERSWITHINFORMATIONNEEDS，ANDVARIOUSOSPROGRAMS）ADBMSCANORGANIZE，PROCESS，ANDPRESENTSELECTEDDATAELEMENTSFROMTHEDATABASETHISCAPABILITYENABLESDECISIONMAKERSTOSEARCH，PROBE，ANDQUERYDATABASECONTENTSINORDERTOEXTRACTANSWERSTONONRECURRINGANDUNPLANNEDQUESTIONSTHATARENTAVAILABLEINREGULARREPORTSTHESEQUESTIONSMIGHTINITIALLYBEVAGUEAND/ORPOORLYDEFINED，BUTPEOPLECAN“BROWSE”THROUGHTHEDATABASEUNTILTHEYHAVETHENEEDEDINFORMATIONINSHORT，THEDBMSWILL“MANAGE”THESTOREDDATAITEMSANDASSEMBLETHENEEDEDITEMSFROMTHECOMMONDATABASEINRESPONSETOTHEQUERIESOFTHOSEWHOARENTPROGRAMMERSINAFILEORIENTEDSYSTEM，USERSNEEDINGSPECIALINFORMATIONMAYCOMMUNICATETHEIRNEEDSTOAPROGRAMMER，WHO，WHENTIMEPERMITS，WILLWRITEONEORMOREPROGRAMSTOEXTRACTTHEDATAANDPREPARETHEINFORMATION4THEAVAILABILITYOFADBMS，HOWEVER，OFFERSUSERSAMUCHFASTERALTERNATIVECOMMUNICATIONSPATHTHEMANAGEMENTINFORMATIONSYSTEM（MIS）CONCEPTHASBEENDEFINEDINDOZENSOFWAYSSINCEONEORGANIZATIONSMODELOFANMISISLIKELYTODIFFERFROMTHATOFANOTHER，ITSNOTSURPRISINGTHATTHEIRMISDEFINITIONSWOULDALSOVARYINSCOPEANDBREADTHFOROURPURPOSES，ANMISCANBEDEFINEDASANETWORKOFCOMPUTERBASEDDATAPROCESSINGPROCEDURESDEVELOPEDINANORGANIZATIONANDINTEGRATEDASNECESSARYWITHMANUALANDOTHERPROCEDURESFORTHEPURPOSEOFPROVIDINGTIMELYANDEFFECTIVEINFORMATIONTOSUPPORTDECISIONMAKINGANDOTHERNECESSARYMANAGEMENTFUNCTIONSMISHASDIFFERENTMODELS，INADDITIONTOWHATMIGHTBETERMEDTHEHORIZONTALMANAGEMENTSTRUCTURE，ANORGANIZATIONISALSODIVIDEDVERTICALLYINTODIFFERENTSPECIALTIESANDFUNCTIONSWHICHREQUIRESEPARATEINFORMATIONFLOWSCOMBININGTHEHORIZONTALMANAGERIALLEVELSWITHTHEVERTICALSPECIALTIESPRODUCESTHECOMPLEXORGANIZATIONALSTRUCTUREUNDERLYINGTHISSTRUCTUREISADATABASECONSISTING，IDEALLY，OFINTERNALLYANDEXTERNALLYPRODUCEDDATARELATINGTOPAST，PRESENT，ANDPREDICTEDFUTUREEVENTS。THEFORMIDABLETASKOFTHEMISDESIGNERISTODEVELOPTHEINFORMATIONFLOWNEEDEDTOSUPPORTDECISIONMAKINGGENERALLYSPEAKING，MUCHOFTHEINFORMATIONNEEDEDBYMANAGERSWHOOCCUPYDIFFERENTLEVELSANDWHOHAVEDIFFERENTRESPONSIBILITIESISOBTAINEDFROMACOLLECTIONOFEXISTINGINFORMATIONSYSTEMS（ORSUBSYSTEMS）THESESYSTEMSMAYBETIEDTOGETHERVERYCLOSELYINANMISMOREOFTEN，HOWEVER，THEYAREMORELOOSELYCOUPLED外文翻译中文数据库系统1数据库系统引论今天，也就是比以往任何时候都更加明显，一个组织的成功取决于它准确而及时地获取关于它运营数据的能力及有效管理这些数据的能力，并用它来分析和指导其活动。一些短语诸如“超级公路信息”已随处可见，信息处理成为一个迅速增长为每年几十亿美元的产业。我们今天能得到的信息实在是爆炸性的，而数据作为一个组织资产的价值正得到广泛的认可。这种议论推动了对强大及灵活的数据库管理系统的不断增长的需要。数据库是一组数据的集合，它可典型地描绘一个或多个相关组织的活动。举例来说，一个大学的数据库可能包含如下信息诸如学生、教职员、课程及班组等实体。实体间的关系，诸如学生课程名册、教员教授课程以及课程使用教室。一个数据库管理系统（或称DBMS）是一种旨在协助维护和使用大型数据集合的软件，为这些系统所需要，同时为了它们的使用，DBMS发展很迅速；举例来说，在文件中存储数据须书写特定的应用代码来管理它。一般来说，数据库管理系统领域是计算机科学的一个缩影。它所要解决的问题及使用的技术包括了广泛的范围，这包括语言、面向对象及其他的编程变化方法、编译、操作系统、并发编程、数据结构、算法理论、并行及分布式系统、用户接口、专家系统及人工智能、统计技术以及动态编程。随着愈来愈多的数据能进入在线及通过计算机网络变得从未有过的便于存取，数据库管理系统将继续增加其重要性。今天这个领域正在为激动人心的多媒体数据库、交互电视、数字图书馆及许多科学工程（诸如人类基因图工程以及NASA的地球观测工程）及许多公司为巩固它们的决策处理愿望和为了挖掘它们自己公司的有用信息的数据仓库等所推动。在商业方面，数据库管理系统代表了一个最大和最强劲的市场份额，对数据库管理系统的研究将被证明能在多个方面而不是一个方面得到丰厚的回报。2数据库概述一个数据库由一个文件或文件集合组成。这些文件中的信息可分解成一个个记录，每个记录有一个或多个域。域是数据存储的基本单位，每个域一般含有由数据库描述的属于实体的一个方面或一个特性的信息。用户使用键盘和各种排序命令，能够快速查找、重排、分组并在查找的许多记录中选择相应的域，建立特定集上的报表。数据库记录和文件的组织必须确保能对信息进行检索。早期的系统是顺序组织的如字母顺序、数字顺序或时间顺序直接访问存储设备的研制成功使得通过索引随机访问数据成为可能。用户检索数据库信息的主要方法是QUERY查询。通常情况下，用户提供一个字符串，计算机在数据库中寻找相应的字符序列，并且给出字符串在何处出现。比如，用户能够在所有记录中寻找所有LASTNAME域为SMITH的记录。在非结构化的数据库中，按照实体的一个简单列表组织记录很多个人计算机的简易数据库是非结构的。层次型数据库按树型组织记录，每一层的记录分解成更小的属性集。层次型数据库在不同层的记录集之间提供一个单一链接，与此不同，网络型数据库在不同记录集之间提供多个链接，这是通过设置指向其它记录集的链或指针来实现的。网络型数据库的速度及多样性使其在企业中得到广泛应用。当文件或记录间的关系不能用链表达时，使用关系型数据库。一个表或一个“关系”，就是一个简单的非结构列表。多个关系可通过数学关系提供所需信息。面向对象的数据库存储并处理更复杂的称为对象的数据结构，可组织成有层次的类，其中的每个类可以继承层次链中更高一级类的特性，这种数据库结构最灵活，最具适应性。3关系数据库的结构关系模型是任何关系数据库管理系统（RDBMS）的基础。一个关系模型有二个核心组件对象或关系的集合，作用于对象或关系上的操作，以及数据完整性规则。换句话说，关系数据库有一个存储数据的地方，一种创建和检索数据的方法，以及一种确认数据的逻辑一致性的方法。一个关系数据库使用关系或二维表来存储支持某个事物所需的信息。让我们了解一下一个传统的关系数据库系统的基本组件并且学习如何设计一个关系数据库。一旦你对于行、列、表和关联是什么有了深刻理解，你就能够充分发挥关系数据库的强大功能。31表，行和列在关系数据库中，一