毕业论文外文翻译MySQL数据库管理中心.docx
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毕业论文外文翻译MySQL数据库管理中心.docx
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毕业论文外文翻译MySQL数据库管理中心
ManagementCenterofMySQL
Authors:
Lauderdale,John
Tsang,DannyH.K.
Baciu,George
IssueDate:
2006
Citation:
ProceedingsofIEEEVisual'96,Melbourne,Australia,February2006,p.447-458
Database(sometimesspelleddatabase)isalsocalledanelectronicdatabase,referringtoanycollectionsofdata,orinformation,thatisspeciallyorganizedforrapidsearchandretrievalbyacomputer.Databasesarestructuredtofacilitatethestorage,retrieval,modificationanddeletionofdatainconjunctionwithvariousdata-processingoperations.Databasecanbestoredonmagneticdiskortape,opticaldisk,orsomeothersecondarystoragedevice.
Adatabaseconsistsofafileorasetoffiles.Theinformationinthethesefilesmaybebrokendownintorecords,eachofwhichconsistsofoneormorefieldsarethebasicunitsofdatastorage,andeachfieldtypicallycontainsinformationpertainingtooneaspectorattributeoftheentitydescribedbythedatabase.Usingkeywordsandvarioussortingcommands,userscanrapidlysearch,rearrange,group,andselectthefieldsinmanyrecordstoretrieveorcreatereportsonparticularaggregatesofdata.
Databaserecordsandfilesmustbeorganizedtoallowretrievaloftheinformation.Earlysystemwerearrangedsequentially(i.e.,alphabetically,numerically,orchronologically);thedevelopmentofdirect-accessstoragedevicesmadepossiblerandomaccesstodataviaindexes.Queriesarethemainwayusersretrievedatabaseinformation.Typicallytheuserprovidesastringofcharacters,andthecomputersearchesthedatabaseforacorrespondingsequenceandprovidesthesourcematerialsinwhichthosecharactersappear.Ausercanrequest,forexample,allrecordsinwhichthecontentofthefieldforaperson’slastnameisthewordSmith.
Inflatdatabases,recordsareorganizedaccordingtoasimplelistofentities;manysimpledatabasesforpersonalcomputersareflatinstructure.Therecordsinhierarchicaldatabasesareorganizedinatreelikestructure,witheachlevelofrecordsbranchingoffintoasetofsmallercategories.Unlikehierarchicaldatabases,whichprovidesinglelinksbetweensetsofrecordsatdifferentlevels,networkdatabasescreatemultiplelinkagesbetweensetsbyplacinglinks,orpointers,toonesetofrecordsinanother;thespeedandversatilityofnetworkdatabaseshaveledtotheirwideuseinbusiness.Relationaldatabasesareusedwhereassociationsamongfilesorrecordscannotbeexpressedbylinks;asimpleflatlistbecomesonetable,or“relation”,andmultiplerelationscanbemathematicallyassociatedtoyielddesiredinformation.Object-orienteddatabasesstoreandmanipulatemorecomplexdatastructures,called“objects”,whichareorganizedintohierarchicalclassesthatmayinheritpropertiesfromclasseshigherinthechain;thisdatabasestructureisthemostflexibleandadaptable.
Theinformationinmanydatabasesconsistsofnatural-languagetextsofdocuments;Smalldatabasescanbeusedbyindividualsathome.Theseandlargerdatabaseshavebecomeincreasinglyimportantinbusinesslife.Typicalcommercialapplicationsincludeairlinereservations,productionmanagement,medicalrecordsinhospitals,andlegalrecordsofinsurancecompanies.Thelargestdatabasesareusuallymaintainedbygovernmentalagencies,businessorganizations,anduniversities.Thesedatabasesmaycontaintextsofsuchmaterialsascatalogsofvariouskinds.Referencedatabasescontainbibliographiesorindexesthatserveasguidestothelocationofinformationinbooks,periodicals,andotherpublishedliterature.Thousandsofthesepubliclyaccessibledatabasesnowexist,coveringtopicsrangingfromlaw,medicine,andengineeringtonewsandcurrentevents,games,classifiedadvertisements,andinstructionalcourses.Professionalssuchasscientists,doctors,lawyers,financialanalysts,stockbrokers,andresearchersofalltypesincreasinglyrelyonthesedatabasesforquick,selectiveaccesstolargevolumesofinformation.
DBMSStructuringTechniques
Sequential,direct,andotherfileprocessingapproachesareusedtoorganizeandstructuredatainsinglefiles.ButaDBMSisabletointegratedataelementsfromseveralfilestoanswerspecificuserinquiriesforinformation.Thatis,theDBMSisabletostructureandtietogetherthelogicallyrelateddatafromseverallargefiles.
LogicalStructures.Identifyingtheselogicalrelationshipsisajobofthedataadministrator.Adatadefinitionlanguageisusedforthispurpose.TheDBMSmaythenemployoneofthefollowinglogicalstructuringtechniquesduringstorage,access,andretrievaloperations.
Liststructures.Inthislogicalapproach,recordsarelinkedtogetherbytheuseofpointers.Apointerisadataiteminonerecordthatidentifiesthestoragelocationofanotherlogicallyrelatedrecord.Recordsinacustomerm
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