Ifomu lesithathu evamile (3NF) yisimiso se-database esisekela ubuqotho bemininingwane ngokwakhiwa kwemigomo yokugcina imininingwane ehlinzekwe yiFomu Ejwayelekile Yokuqala (i-1NF) neFomu Elibili Elijwayelekile (2NF).
Izidingo zeFomu Eyesithathu Ejwayelekile
Kunezidingo ezimbili eziyisisekelo ze-database ukuze zibe kwifomu lesithathu evamile:
- I-database kufanele ihlangabezane nezidingo zombili 1NF no- 2NF .
- Wonke amakholomu wedatha kumele athembele kunkinobho eyinhloko , okusho ukuthi noma yiliphi inani lekholomu lingawuthola ukhiye oyinhloko kuphela.
Mayelana ne-Dependence Yesikhiye Esiyinhloko
Ake sihlole kabanzi ukuthi sisho ukuthini ukuthi zonke izinsika kumele zithembele ekhiye oyinhloko.
Uma inani lekholomu lingatholakala kusukela kokubili ukhiye oyinhloko kanye nelinye ikholomu etafuleni, liphula i-3NF. Cabanga ngethebula labaSebenzi elinamakholomu:
- I-EmployeeID
- Igama
- Isibongo
Ingabe kokubili i-LastName ne-FirstName incike kuphela kubaluleka be-EmployeeID? Yebo, ingabe i-LastName ingabe ixhomeke ku-FirstName? Cha, ngoba akukho lutho oluvela ku-LastName oluzophakamisa ukubaluleka kokuqala kwegama. I-FirstName ingabe ixhomeke ku-LastName? Awukho futhi, ngoba okufanayo kuyiqiniso: noma yikuphi igama lokugcina elingase libe khona, alikwazanga ukunikeza ukusikisela kokubaluleka kokuqala kwegama. Ngakho-ke, leli tafula lihambisana ne-3NF.
Kodwa cabanga ngalolu daba Imoto:
- I-VehicleID
- Umkhiqizi
- Isibonelo
Umkhiqizi kanye noModeli bangathola ku-VehicleID - kodwa i-Model ingathola futhi kuMkhiqizi ngoba imodeli yemoto eyenziwa ngumenzi othile kuphela. Lo mklamo wetafula awuhambisani ne-3NF, ngakho-ke, kungabangela ukuhlukunyezwa kwedatha. Isibonelo, ungase ubuyekeze umenzi ngaphandle kokubuyekeza imodeli, ukwethula ukungalungi.
Ukwenza kube okuhambisanayo, sidinga ukuhambisa ikholomu elisekelwe kwelinye itafula bese silibhekisela ngokusebenzisa ikhi langaphandle. Lokhu kuzoholela ematafuleni amabili:
Izimoto Ithebula
Etafuleni elingezansi, i-ModelID ikhiye wangaphandle kuthebula leModeli:
- I-VehicleID
- Umkhiqizi
- ModelID
Amathebula Ithebula
Lezi zimodeli zamamephu wamatafula amasha kubakhiqizi. Uma ufuna ukuvuselela noma yiluphi ulwazi lwezimoto oluthile olufanekisela imodeli, ungayenza kule tafula, kunokuba uphendule emotweni.
- ModelID
- Umkhiqizi
- Isibonelo
Amasimu ahlulwe ku-3NF Model
Itafula lingase libe nomkhakha otholwe - owodwa obalwa ngokusekelwe kwamanye amakholomu etafuleni. Isibonelo, cabangela leli thebula lemiyalo yewijethi:
- Inombolo Ye-oda
- Inombolo yekhasimende
- Intengo yokukodwa
- Inani
- Inani
Ukuhlukana okuphelele kwe-3NF ngoba kungathathwa ngokuphindaphinda inani lentengo ngobuningi, kunokuba ixhomeke ngokugcwele ekhiye oyinhloko. Kumelwe sisuse etafuleni ukuze sithobele ifomu lesithathu evamile.
Eqinisweni, njengoba isuselwe, kungcono ukuthi ungaligcinanga ku-database nakancane.
Singakwazi ukuyiqhathanisa "ngendiza" lapho senza imibuzo egciniwe. Isibonelo, kungenzeka ukuthi sisebenzise le mbuzo ngaphambilini ukuthola izinombolo ze-oda nezinombolo:
Hlunga inani le-oda, inani elivela ku-WidgetOrdersManje singasebenzisa umbuzo olandelayo:
Hlunga iNombolo ye-Order, UnitPrice * Inani le-AS Total FROM WidgetOrdersukuze kufinyelele imiphumela efanayo ngaphandle kokuphula imithetho yokujwayelekile.