Iyini i-Boyce-Codd Form Normal (BCNF)?

I-BCNF iyanciphisa ubugebengu futhi ikhulise ubuqotho bemininingwane

Umgomo weFomu le-Boyce-Codd Normal (BCNF) ukwandisa ubuqotho bemininingwane ngokuhlela amakholomu namatafula wesitatimende esivumelanayo ukuze kufezekiswe ukusimamisa idatha. Ukumiswa kwe-database kwenzeka uma kukhona ubuhlobo obukhona phakathi kwamatafula futhi uma amatafula echazile imithetho yokwenza i-database ibe yinkimbinkimbi futhi igcine idatha.

Imigomo yemigomo yokugcina idatha iwukuqeda idatha ehlukumezayo nokuqinisekisa ukuthi ukuxhomeka kwedatha kunengqondo.

I-database isejwayelekile uma idatha efanayo ingagcinwa etafuleni elingaphezu kweyodwa futhi uma idatha ehlobene kuphela igcinwe etafuleni.

Umsuka we-Boyce-Codd Ifomu Ejwayelekile

Ukulandela uchungechunge lwemikhombandlela kuqinisekiswe ukuthi imininingwane yolwazi iyajwayelekile. Lezi ziqondiso zibhekwa njengezifomu ezivamile futhi zibalwa kusukela ku-one kuya kwezihlanu. Idatha yokuxhumana echazwa njengesijwayelekile uma ihlangabezana namafomu amathathu okuqala: 1NF, 2NF, ne-3NF.

I-BCNF yasungulwa njenge-extension kwifomu yesithathu evamile, noma i-3NF, ngo-1974 nguRaymond Boyce no-Edgar Codd. La madoda ayesebenza ukudala ama-database azinqunyelwe ukuqeda i-redundancies ngenhloso yokunciphisa isikhathi sokufunda. Ifomu lesithathu evamile lisusa amakholomu angaxhomeki ekhiye oyinhloko ngaphezu kokuhlangana nemihlahlandlela emafomu okuqala nesesibili avamile. I-BCNF, ngezinye izikhathi ebizwa ngokuthi i-3.5NF, ihlangabezana nazo zonke izidingo ze-3NF futhi idinga ukuthi izikhiye zokukhethwa zingabi nokuthembela kwezinye izici etafuleni.

Ngesikhathi sokudalwa kwe-BCNF, u-Boyce wayengomunye wabakhi abakhulu beLimi Oluhlelekile Lwemibuzo YesiNgisi (SQL), okwenza ngcono ukubuyiswa kwedatha ngokusebenzisa imodeli yohlobo lweCodd. Kulo modeli, i-Codd yenze ukuthi lokho okubunzima kwezakhiwo kwakungancishiswa, okwakusho ukuthi imibuzo ingaba namandla futhi iguquguquke.

Ngokusebenzisa imininingwane yakhe yokuxhumana, i-Codd ichaza i-1NF, 2NF, ne-3NF imihlahlandlela. Wabambisana no-Boyce ukuze achaze i-BCNF.

Amakhidi Okhethiwe ne-BCNF

Ukhiye wokukhethwa kukho ikholomu noma inhlanganisela yamakholomu etafuleni okwenza ukhiye oyingqayizivele ku-database. Ukuhlanganiswa kwezimfanelo kungasetshenziselwa ukukhomba irekhodi lesisekelo ngaphandle kokubhekisela kunoma iyiphi enye idatha. Ithebula ngalinye lingabandakanya izinkinobho eziningi zokukhethwa, noma yiziphi zazo ezingafanelekela njengekhikhi eyinhloko. Itafula liqukethe ukhiye owodwa oyinhloko.

Izihluthulelo zokukhetha kumele zihlukile.

Ubuhlobo bukhona ku-BCNF uma zonke izici eziyinhloko ziyizihluthulelo. Cinga itafula lemininingwane egciniwe eligcina ulwazi lomsebenzi futhi linemfanelo ethi , , , futhi