??????????????????????????ò??????????????鱾????θ????顣????????????????????????????????????????????????1?????????淶?????????????????????????????????????????????????????????????淶????????????????????????????????????????????????????????????????????????????????????
????1????????????????
???????X->Y??????Y??????X???????X->Y?????????????????
????2??????????????
???????X->Y????Y????X???????X->Y????????????????
????3?????????????
??????R??U???У????X->Y???????κ????X???κ??????X'??????X‘???????Y?????Y??X?????????????
????4?????????????
???????X->Y????Y???????????X?????Y??X?????????????
????5??????????
??????R??U??F?????????X->Y?? Y??????X??Y->Z?????Z??X?????????????
????-> ??????  XX????XX
?????淶??
?????????????????????????????????????????????? 1NF??2NF??3NF??BCNF??4NF??5NF?????????????????3NF????????????о? ?3???????????????????????????????????????????????????????
????1NF(??????)
?????????????????壬??????????R???????????????????????????????????????ж?????????β?????????R?????????????????????????????????????????
????FIRST(SNo??SName??Status??City??Pno??Qty)
????F = {Sno->Sname??Sno->Status??Status->City??(Sno??Pno)->Qty} ????????????????????????????????????????????????
????????????????1NF???????????????ж???
????????????????R????Address?????????????????Province??City??County etc.???????????????????
????2NF(??????)
????2NF????1NF??????????????????????1NF??????????????????????????????????????????????е??????????
????FIRST????е?????Sno??Pno????Sno->Status????????????Status??????????????????2NF??
?????????????FIRST???????????FIRST1(Sno??Sname??Status??City)??FIRST(Sno??Pno??Qty).???????FIRST1?????SNo???????????????????Sno??????????2NF??FIRST2?????SNo??Pno??????????Qty?????????Sno??Pno???????????2NF??
????3NF(???????)
???????????????2NF?????????????????????????????????????????????????????Sno->Status??Status->City????????????????????????????????3NF??
?????????2NF?????????ν??л???FIRST1(Sno??Sname??Status)   FIRST2(Status??City)   FIRST3(Sno??Pno??Qty)???????????????????????????????????????????塣???????????????????????? 5NF ∈4NF  ∈BCNF ∈3NF∈ 2NF∈ 1NF????Χ????С???????????????????????????????????????????????????????????????????????????????????????????????????????????3NF??????????????????????????????????????????й????????е?????????????????о???????????????????????????????????????е???????????????????????е???????????ɡ??????????????????????????