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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
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