Ukuxhomekeka kwe-Database kuyinto isihloko esivame ukudidela bobabili abafundi nabagcini bezinhlelo ezifanayo. Ngenhlanhla, akuzona lokho okuyinkimbinkimbi futhi kungabonakaliswa kangcono ngokusebenzisa izibonelo ezimbalwa. Kulesi sihloko, sihlola izinhlobo ezijwayelekile zokuxhaswa kwedatha.
I-Dependency Dependencies / Ukuxhomeka Kwemisebenzi
Ukuthembela kwenzeka ku-database uma ulwazi olugciniwe etafuleni elifanayo lemininingwane yolwazi lugcina ngokukhethekile olunye ulwazi olugcinwe kuthebula elifanayo. Ungaphinda uchaze lokhu njengobudlelwane lapho ukwazi khona inani lesikhangiso esisodwa (noma isethi yezimfanelo) okwanele ukukutshela inani lenye isici (noma isethi yezimfanelo) kuthebula elifanayo.
Ukusho ukuthi kuncike phakathi kwezimfanelo etafuleni kufana nokuthi kuncike ekusebenzeni phakathi kwalezi zimfanelo. Uma kuncike ekutheni imininingwane efana nokuthi isici B sixhomeke kumbono A, ungabhala lokhu ngokuthi "A -> B".
Isibonelo, Etafuleni lokufaka izici zesevisi ezibandakanya iNombolo Yokuphepha Komphakathi (SSN) negama, kungashiwo ukuthi igama lixhomeke ku-SSN (noma i-SSN -> igama) ngoba igama lomsebenzi lingagunyazwa ngokukhethekile kwi-SSN yabo. Kodwa-ke, isitatimende esilandelayo (igama -> SSN) alilona iqiniso ngoba abasebenzi abangaphezu kwesinye bangaba negama elifanayo kodwa ama-SSN ahlukile.
Ukuxhomekeka Okungasebenzi Okungeyona Imisebenzi
Ukuthembela okuncane okusebenzayo kwenzeka uma uchaza ukuxhomekeka okusebenzayo kwesici kwiqoqo lezimfanelo ezifaka imfanelo yokuqala. Isibonelo, i- "{A, B} -> B" iyincike ekusebenzeni okuncane, njengoba "{igama, SSN} -> SSN". Lolu hlobo lokuxhomekeka kokusebenza lubizwa ngokuthi luyingcosana ngoba lungatholakala ekuhlakanipheni okuvamile. Kusobala ukuthi uma usuvele uyakwazi ukubaluleka kweB, khona-ke inani le-B lingakunqunywa ngokulinganayo yilo lwazi.
Ukuxhomeka Okugcwele Okusebenzayo
Ukuxhomekeka okugcwele kokusebenza kwenzeka uma usuvele uhlangabezana nezidingo zokuxhomekeka kokusebenza futhi isethi yezimfanelo ngakwesobunxele besitatimende sokuxhomeka emsebenzini asikwazi ukunciphisa noma yikuphi okunye. Isibonelo, i- "{SSN, age} -> igama" incike ekusebenzeni, kodwa akusiyo ukuxhomeka okugcwele kokusebenza ngoba ungasusa iminyaka kusukela kwesokunxele sesitatimende ngaphandle kokuthinta ubudlelwane bokuthembela.
Ukuthembela Okuguquguqukayo
Ukuthembela okuguquguqukayo kwenzeka uma kukhona ubudlelwane obungavamile obubangela ukuxhomekeka okusebenzayo. Isibonelo, i- "A -> C" iyinciko yokuguqula lapho kuyiqiniso kuphela ngoba kokubili "A -> B" no "B -> C" kuyiqiniso.
Ukuxhomeka Okumangalisayo
Ukuxhomekeka okunamandla kunokwenzeka lapho ukutholakala komugqa owodwa noma ngaphezulu etafuleni kubonisa ukuba khona komunye noma imigqa eminye etafuleni elifanayo. Ngokwesibonelo, cabanga inkampani yemoto eyenza izinhlobo eziningi zemoto, kodwa njalo yenza imibala ebomvu neluhlaza okwesimodeli ngasinye. Uma unetafula eliqukethe igama lemodeli, umbala nonyaka wemoto ngayinye inkampani eyenza yona, kuncike ekuthembekeni okuningi kuletafula. Uma kunomugqa wegama elithile lemodeli nonyaka oluhlaza okwesibhakabhaka, kuzomele kube nomugqa ofanayo ohambisana nengubo ebomvu yemoto efanayo.
Ukubaluleka Kwezindinganiso
Ukuxhomeka kokuxhomekeka kwedatha kubalulekile ukuqonda ngoba banikeza amabhlogo wokwakha ayisisekelo asetshenziselwa ukusimamisa idatha . Ngokwesibonelo:
- Ukuze itafula libe kwifomu yesibili evamile (2NF) , akumele kube khona isimo se-non-prime imfanelo etafuleni esebenze ngokusekelwe esigatshaneni somkhiqizo wokhetho .
- Ukuze itafula libe kwifomu lesithathu evamile (3NF) , yonke imfanelo engeyona eyinhloko kumele ibe nokuxhomekeka okusebenzayo okungekho okuguquguqukayo kuwo wonke ukhiye we-candidate.
- Ukuze itafula libe yifomu le-Boyce-Codd Normal (BCNF) , zonke izici zokusebenza ezisebenzayo (ngaphandle kokuthembela okuncane) kumele zibe kwi- superkey .
- Ukuze itafula libe kwifomu lesine evamile (4NF) , akufanele kube nokuxhomekeka okuningi.