《数据库系统原理教学课件》作业讲评课件.ppt

1,作业讲评,p30,2,2.4.3 a,class,country(bore16(Classes),3,2.4.3 b,name(launched1921(Ships),4,2.4.3 c,ship(battle=North Atlantic AND result=sunk(outcomes),5,2.4.3 d,name(displacement35000 AND launched1921(Classes Ships),6,2.4.3 e,name,numGun,displacement(battle=Guadalcanal(Outcomes)Ships Classes),7,2.4.3 f,name(Ships)name(ship(Outcomes),8,2.4.3 g,R1(name,class):=name,class(Ships)R2:=R1Answer(class):=class(R1)-class(R1 R2)R1.class=R2.class AND R1.name R2.name,9,2.4.3 h,country(type=bb(Classes)country(type=bc(Classes),10,2.4.3 i,S1(ship,date,result):=ship,date,result(Outcomes Battles)Outcomes.battle=Battles.nameS2(ship,date,result):=result=damaged(S1)Answer(ship):=ship(S2 S1)S2.ship=S1.ship AND S2.dateS1.date,