Theentity-relationship(E-R)datamodelisbasedonaperceptionofarealworldthatconsistsofaclletionofbasicobjects,called(请作答此空)，andofrelationshipsamongtheseobjects.Anentityisa“thing”or"object"intherealworldthatisdistinguishablefromotherobjects.Entitiesaredescribedinadatabasebyasetof():Arelationshipisanassociationamongseveralentities.Thesetofallentitiesofthesametypeandthesetofallrelationshipsoftheametypearetermedanentitysctandrelationshipset,respectively.Theoveralllogicalstructure(schema)ofadatabasecanbeexpressedgraphicallybyanE-Rdiagram,whichisbuiltupfromthefllowingcomponents:()represententityset,()representatributes,ete.Inadditiontoentitiesandrelations,theE-Rmodelrepresentscertain()towhichthecontentsofadatabasemustconform.Theentity-relationshipmodeliswidelyusedindatabasedesign.
A.data
B.things
C.entities
D.objects
正确答案是C