计算机科学导论课件：databases.ppt

Chapter9

Databases

ObjectivesUnderstandaDBMSanddefineitscomponents.UnderstandthearchitectureofaDBMSanditslevels.Distinguishbetweendifferentdatabasemodels.Understandtheconceptofrelationaldatabaseoperationsonarelation.UseStructuredQueryLanguage(SQL)todefinesimplerelations.

DatabasesandDBMSAdatabaseisacollectionofdatathatislogically,butnotnecessarilyphysically,coherent.Adatabasemanagementsystemdefines,creates,andmaintainsadatabase.Italsoallowsuserscontrolledaccesstodatainthedatabase.

DBMScomponents

Databasearchitecture

DBmodels-hierarchical

DBmodels–network

DBmodel-relational

RelationArelation,inappearance,isatwo-dementionaltable.

SQLThestructuredquerylanguageisthestandardizedlanguageweusetooperateonrelationaldatabases.Itisadeclarative(notprocedural)language,whichmeansthattheusersdeclarewhattheywantwithouthavingtowriteastep-by-stepprocedure.

Operationsonrelations-insertinsertintoCOURSES

values(“CIS52”,“TCP/IPProtocols”,6)

Operationsonrelations-deletedeletefromCOURSES

whereNo=“CIS19”

Operationsonrelations-updateupdateCOURSES

setUnit=6

whereNo=“CIS51”

Operationsonrelations-selectselect*

fromCOURSES

whereUnit=5

Operationsonrelations-projectselectNo,Unit

fromCOURSES

Operationsonrelations-joinselectNo,Course-Name,Unit,Professor

fromCOURSES,TAUGHT-BY

whereCOURSES.No=TAUGHT-BY.No

Operationsonrelations-unionselect*

fromCIS15-Roster

unionselect*

fromCIS52-Roster

Operationsonrelations-intersectionselect*fromCIS15-Roster

intersection

select*fromCIS52-Roster

Operationsonrelations-differenceselect*fromCIS15-Roster

minusselect*fromCIS52-Roster

ObjectivesUnderstandaDBMSanddefineitscomponents.UnderstandthearchitectureofaDBMSanditslevels.Distinguishbetweendifferentdatabasemodels.Understandtheconceptofrelationaldatabaseoperationsonarelation.UseSt