I-BCNF iyanciphisa ubuninzi kwaye ikhulise ingqibelelo yedatha
Iinjongo zeFomily-Codd Ifomu eQinisekileyo (BCNF) kukunyusa intembeko yedatha ngokucwangcisa iikholomu kunye neetafile zesiseko sedatha ukuze kufezekiswe ukugcinwa kwedatha. Ukugcinwa kweenkcukacha ngokusemgangathweni kwenzeka xa kukho ubudlelwane obuhle phakathi kwetafile kwaye xa iitheyibhile zichaze imigaqo yokwenza ukuba i-database iguquke ngakumbi kwaye igcine idatha.
Iinjongo zokuqhelaniswa kwedatha ziza kuphelisa idatha ehlukileyo kwaye ukuqinisekisa ukuxhomekeka kwedatha kunengqiqo.
I-database isebenza ngokuqhelekileyo xa idata elifanayo lingagcinwa kwitafile enye kwaye xa kuphela idatha edibeneyo igcinwa etafileni.
Umvelaphi weFomilyce-Codd ifom yesiQhelo
Ukulandela uchungechunge lwezikhokelo kuqinisekisa ukuba iinkcukacha zolwazi ziqhelekileyo. Ezi zikhokelo zibhekiswa njengeifomu eziqhelekileyo kwaye zibalwa ukusuka kwenye ukuya kwezihlanu. Idatha yolwazi echazwe njengesiqhelo xa idibana neefom zokuqala ezintathu: 1NF, 2NF, kunye ne-3NF.
I-BCNF yenziwe njengesandiso kwifomu yesithathu evamile, okanye i-3NF, ngo-1974 nguRaymond Boyce noEdgar Codd. Amadoda ayesebenzela ukudala izikimu zeenkcukacha ezigciniweyo zokunciphisa i-redundancies ngenjongo yokunciphisa ixesha lokubhala. Ifom yesithathu eqhelekileyo isusa iikholomu ezingaxhomekeke kwisitshixo esisisiseko ekudibaniseni ukuhlangabezana nezikhokelo kwiifom zokuqala nezesibili eziqhelekileyo. I-BCNF, edlalwa ngamanye amaxesha njenge-3.5NF, idibana nayo yonke imfuno ye-3NF kwaye idinga ukuba izitshixo zabaviwa zingabi naluphi na ukuxhomekeka kwezinye iimpawu kwitafile.
Ngexesha lokudalwa kwe-BCNF, u-Boyce wayengomnye wabaphuhlisi abaziintloko beeLwimi eziCwangcisiweyo zesiNgesi (SQL), okuphucula ukubuyiswa kwedatha ngokusebenzisa imodeli yohlobo lweCodd. Kulo mzekelo, i-Codd ibonise ukuba ubunzima bezakhiwo zolwazi kuncitshiswa, okubangela ukuba imibuzo ibe namandla kwaye iguquke.
Ukusebenzisa ulwazi lwakhe lweenkcukacha zolwazi, iCodd ichaza i-NN, 2NF, kunye ne-3NF izikhokelo. Wabambisana noBrace ukuba achaze i-BCNF.
Abaviwa abaKhiye kunye ne-BCNF
Inqakrazo yomviwa yikholam okanye inhlanganisela yamakholomu kwitheyibhile eyenza ukhiye obalulekileyo kwiziko. Ukuhlanganiswa kweempawu kungasetyenziselwa ukuchonga irekodi yeenkcukacha ngaphandle kokubhekisela kwiphina idatha. Itheyibhile nganye inokuqulatha izitshixo ezininzi zokubaviwa, naliphi na elikwazi ukufumana ilungelo eliphambili. Itafile iqulethe kuphela ikona ephambili.
Iimpawu ezikhethiweyo mazibe zizodwa.
Ulwalamano oluse-BCNF ukuba yonke i-determinant is key key candidate. Cinga itafile yedatha egcina ulwazi lomsebenzi kwaye ineempawu
Kule tafile, inkundla
Id Employee | Igama lokuqala | Ifani | Isihloko |
13133 | Emily | Smith | UMphathi |
13134 | Jim | Smith | Nxu lumene |
13135 | Emily | Jones | Nxu lumene |
Umncedi oyintloko kule nkcukacha- mgca yi-