大学毕业设计关于数据库外文翻译2篇.doc
- 文档编号:1261256
- 上传时间:2022-10-19
- 格式:DOC
- 页数:25
- 大小:349.50KB
大学毕业设计关于数据库外文翻译2篇.doc
《大学毕业设计关于数据库外文翻译2篇.doc》由会员分享,可在线阅读,更多相关《大学毕业设计关于数据库外文翻译2篇.doc(25页珍藏版)》请在冰豆网上搜索。
重庆理工大学2013届本科生毕业设计(论文)外文文献翻译
原文:
StructureoftheRelationaldatabase
—《DatabaseSystemConcepts》Part1:
RelationalDatabases
Therelationalmodelisthebasisforanyrelationaldatabasemanagementsystem(RDBMS).Arelationalmodelhasthreecorecomponents:
acollectionofobjectsorrelations,operatorsthatactontheobjectsorrelations,anddataintegritymethods.Inotherwords,ithasaplacetostorethedata,awaytocreateandretrievethedata,andawaytomakesurethatthedataislogicallyconsistent.
Arelationaldatabaseusesrelations,ortwo-dimensionaltables,tostoretheinformationneededtosupportabusiness.Let'sgooverthebasiccomponentsofatraditionalrelationaldatabasesystemandlookathowarelationaldatabaseisdesigned.Onceyouhaveasolidunderstandingofwhatrows,columns,tables,andrelationshipsare,you'llbewellonyourwaytoleveragingthepowerofarelationaldatabase.
Tables,Row,andColumns
Atableinarelationaldatabase,alternativelyknownasarelation,isatwo-dimensionalstructureusedtoholdrelatedinformation.Adatabaseconsistsofoneormorerelatedtables.
Note:
Don'tconfusearelationwithrelationships.Arelationisessentiallyatable,andarelationshipisawaytocorrelate,join,orassociatetwotables.
Arowinatableisacollectionorinstanceofonething,suchasoneemployeeoronelineitemonaninvoice.Acolumncontainsalltheinformationofasingletype,andthepieceofdataattheintersectionofarowandacolumn,afield,isthesmallestpieceofinformationthatcanberetrievedwiththedatabase'squerylanguage.Forexample,atablewithinformationaboutemployeesmighthaveacolumncalledLAST_NAMEthatcontainsalloftheemployees'lastnames.Dataisretrievedfromatablebyfilteringonboththerowandthecolumn.
PrimaryKeys,Datatypes,andForeignKeys
TheexamplesthroughoutthisarticlewillfocusonthehypotheticalworkofScottSmith,databasedeveloperandentrepreneur.HejuststartedanewwidgetcompanyandwantstoimplementafewofthebasicbusinessfunctionsusingtherelationaldatabasetomanagehisHumanResources(HR)department.
Relation:
Atwo-dimensionalstructureusedtoholdrelatedinformation,alsoknownasatable.
Note:
MostofScott'semployeeswerehiredawayfromoneofhispreviousemployers,someofwhomhaveover20yearsofexperienceinthefield.Asahiringincentive,Scotthasagreedtokeepthenewemployees'originalhiredateinthenewdatabase.
Row:
Agroupofoneormoredataelementsinadatabasetablethatdescribesaperson,place,orthing.
Column:
Thecomponentofadatabasetablethatcontainsallofthedataofthesamenameandtypeacrossallrows.
You'lllearnaboutdatabasedesigninthefollowingsections,butlet'sassumeforthemomentthatthemajorityofthedatabasedesigniscompletedandsometablesneedtobeimplemented.ScottcreatestheEMPtabletoholdthebasicemployeeinformation,anditlookssomethinglikethis:
NoticethatsomefieldsintheCommission(COMM)andManager(MGR)columnsdonotcontainavalue;theyareblank.Arelationaldatabasecanenforcetherulethatfieldsinacolumnmayormaynotbeempty.Inthiscase,itmakessenseforanemployeewhoisnotintheSalesdepartmenttohaveablankCommissionfield.ItalsomakessenseforthepresidentofthecompanytohaveablankManagerfield,sincethatemployeedoesn'treporttoanyone.
Field:
Thesmallestpieceofinformationthatcanberetrievedbythedatabasequerylanguage.Afieldisfoundattheintersectionofarowandacolumninadatabasetable.
Ontheotherhand,noneofthefieldsintheEmployeeNumber(EMPNO)columnareblank.Thecompanyalwayswantstoassignanemployeenumbertoanemployee,andthatnumbermustbedifferentforeachemployee.Oneofthefeaturesofarelationaldatabaseisthatitcanensurethatavalueisenteredintothiscolumnandthatitisunique.TheEMPNOcolumn,inthiscase,istheprimarykeyofthetable.
PrimaryKey:
Acolumn(orcolumns)inatablethatmakestherowinthetabledistinguishablefromeveryotherrowinthesametable.
NoticethedifferentdatatypesthatarestoredintheEMPtable:
numericvalues,characteroralphabeticvalues,anddatevalues.
Asyoumightsuspect,theDEPTNOcolumncontainsthedepartmentnumberfortheemployee.Buthowdoyouknowwhatdepartmentnameisassociatedwithwhatnumber?
ScottcreatedtheDEPTtabletoholdthedescriptionsforthedepartmentcodesintheEMPtable.
TheDEPTNOcolumnintheEMPtablecontainsthesamevaluesastheDEPTNOcolumnintheDEPTtable.Inthiscase,theDEPTNOcolumnintheEMPtableisconsideredaforeignkeytothesamecolumnintheDEPTtable.
Aforeignkeyenforcestheconceptofreferentialintegrityinarelationaldatabase.Theconceptofreferentialintegritynotonlypreve
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 大学 毕业设计 关于 数据库 外文 翻译