数据库管理系统概述英文版课件：2 ER Diagram.pptx

COMP231COMP2311ERDiagram

Entity-RelationshipModelCOMP2312 Entity-Relationship(ER)modelisapopularconceptualdatamodel. Thismodelisusedinthedesignofdatabaseapplications Themodeldescribesdatatobestoredandtheconstraintsoverthedata. E-Rmodelviewstherealworldasacollectionofentitiesandrelationshipsamongentities.

OutlineEntityRelationshipBinaryrelationshipWeakEntity/StrongEntityClassHierarchyRelationshipNon-BinaryrelationshipCOMP2313

EntitiesandattributesCOMP2314 AnentityisanobjectintherealworldthatisdistinguishablefromotherobjectsE.g.,AclassroomAteacherTheaddressoftheteacher

Entitiesandattributes Anentityisdescribedusingasetofattributeswhosevaluesareusedtodistinguishoneentityfromanotherofsametypename=ChanTaiManCOMP2315address=25,SiuRoad,Shatinage=55phone=1234-5667

Entitiesandattributes Anentitysetisacollectionofentitiesofthesametypee1(ChanTaiMan,55,…)e2(CheungTin,20,…)e3(WongKing,33,…)COMP2316

Entitiesandattributes Allentriesinagivenentitysethavethesameattributes(thevaluesmaybedifferent).employee=(name,address,age,phone)employee1 employee2name=ChanTaiManaddress=25,SiuRoad,Shatinage=55phone=1234-5667name=CheungTinaddress=25,BigStreet,ShatinCOMP2317age=20phone=2338-7779

COMP2318ERDiagram TheERmodelcanbepresentedgraphicallybyanERdiagramageEmployeenameaddressphoneentityattribute

COMP2319DifferentattributetypesSimpleattributeCompositeattributeMulti-valuedattributeDerivedattribute

SimpleattributeSimpleattributecontainsasinglevalueagenameaddressphoneEmployeeattributeCOMP231entity10

CompositeattributeCompositeattributeContainsseveralcomponentsagenameaddressphonestreetcitycountryEmployeeattributeCOMP231entity11

Multi-valuedattributeMulti-valuedattributeContainsmorethanonevalueagenameaddressphonestreetcitycountryDoubleovalsEmployeeattributeCOMP231entity12

DerivedattributeD