Ubudlelwano beDatabase

Ubuhlobo be-database buyisiphazamiso sabo bonke imininingwane yolwazi

Ubuhlobo buyasungulwa phakathi kwamatafula amabili wedatha uma ithebula elilodwa linokhiye wangaphandle okhombisa ukhiye oyinhloko wenye itafula. Lona umqondo oyisisekelo ngemuva kwedatha yokuxhumana ngegama.

Indlela Ukhiye Wangaphandle Osebenza Ngayo Ukuqala Ubuhlobo

Ake sibukeze izisekelo eziyisisekelo eziyinhloko nakwamanye amazwe. Ikhiye eliyinhloko likhomba kuphela irekhodi ngalinye etafuleni. Luhlobo lwenkinobho yokukhetha ukuthi ngokuvamile ikholomu yokuqala etafuleni futhi ingenziwa ngokuzenzakalelayo yi-database ukuqinisekisa ukuthi ihlukile.

Isihluthulelo sangaphandle singenye ikhiye lokukhetha (hhayi ukhiye oyinhloko) osetshenziselwa ukuxhumanisa irekhodi nedatha kwelinye itafula.

Isibonelo, cabanga ngalezi zibhebhe ezimbili ezikhomba ukuthi uthisha ufundisa yiphi inkambo.

Lapha, ukhiye oyinhloko wetafula wezinkundla yi-Course_ID. Isihluthulelo saso sangaphandle nguMfundisi_ID:

Ungabona ukuthi ukhiye wangaphandle ku-Courses ufanisa ukhiye oyinhloko kubafundisi:

Singasho ukuthi ukhiye wangaphandle we-Teacher_ID usisize ukudala ubuhlobo phakathi kwamaKhosi kanye namatafula abafundisi.

Izinhlobo zeDatabase Ubudlelwano

Ukusebenzisa okhiye abangaphandle, noma ezinye izihluthulelo zokukhetha, ungaqalisa izinhlobo ezintathu zobuhlobo phakathi kwamatafula:

Ngomunye nomunye : Lolu hlobo lobuhlobo luvumela irekhodi elilodwa kuphela ohlangothini ngalunye lobuhlobo.

Ukhiye oyinhloko uhlose irekhodi elilodwa - noma alikho - kwelinye itafula. Isibonelo, emshadweni, umlingani ngamunye unomunye oyedwa. Lolu hlobo lobuhlobo lungasetshenziswa etafuleni elilodwa ngakho-ke alisebenzisi ukhiye wangaphandle.

Inye kuya kokuningi : Ubuhlobo obunye kuya kokuningi buvumela irekhodi elilodwa kuthebula elilodwa ukuthi lihlobene namarekhodi amaningi kwelinye itafula.

Cabanga ngebhizinisi elinesitatimende esinamakhasimende namathebula e-oda.

Ikhasimende elilodwa lingathenga ama-oda amaningi, kodwa i-oda elilodwa alikwazanga ukuxhunyaniswa namakhasimende amaningi. Ngakho-ke ithebula le-oda lizoba nesihluthulelo sangaphandle esilinganisa ukhiye oyinhloko wetafula lamakhasimende, kuyilapho ithebula lamakhasimende lingenalo ukhiye wangaphandle okhomba etafuleni le-oda.

Abaningi kuya kokuningi : Lokhu kubuhlobo obuyinkimbinkimbi lapho amarekhodi amaningi etafuleni angaxhuma kumarekhodi amaningi kwelinye itafula. Isibonelo, ibhizinisi lethu cishe akudingi kuphela Amakhasimende namathebula amarekhodi, kodwa kungenzeka futhi adinga ithebula lemikhiqizo.

Futhi, ubuhlobo phakathi kwamakhasimende kanye netafula ze-Orders kunomuntu oyedwa kuya kokuningi, kodwa cabangela ubuhlobo phakathi kwethebula le-oda nemiyalo. Umyalelo ungaqukatha imikhiqizo eminingi, futhi umkhiqizo ungaxhunyaniswa nemiyalo eminingi: amakhasimende amaningana angathumela i-oda equkethe ezinye imikhiqizo efanayo. Lolu hlobo lobuhlobo ludinga ngamatafula amancane amathathu.

Yini i-Database Relationships ebalulekile?

Ukwakha ubudlelwane obunjalo phakathi kwamatafula e-database kusiza ukuqinisekisa ukuthembeka kwedatha, okufaka isandla esimisweni sokugcina idatha. Isibonelo, kuthiwani uma singazange sixhumanise nanoma yimaphi amatafula ngokusebenzisa ukhiye wangaphandle futhi esikhundleni salokho nje sihlanganise idatha kumatafula e-Courses and Teachers, njengawo:

Lo mklamo ungenakulinganiswa futhi uphula umthetho wokuqala we-database, ifomu yokuqala ejwayelekile (1NF), okusho ukuthi iseli ngalinye letafula kufanele libe neyodwa yedatha ehlukanisiwe yedatha.

Noma mhlawumbe sinqume ukwengeza irekhodi lesibili likaCarmen, ukuze kuqinisekiswe i-NN:

Lokhu kusengumklamo obuthakathaka, ukwethula ukuphindaphinda okungadingekile nokuthi yini ebizwa ngokuthi i- anomalies yokufakela idatha , okusho ukuthi kungabamba iqhaza kwimininingwane engavumelani.

Isibonelo, uma uthisha enamarekhodi amaningi, kuthiwani uma idatha ethile idinga ukuhlelwa, kodwa umuntu owenza ukuhlela idatha akaqapheli ukuthi kukhona amarekhodi amaningi? Ithebula lizoba nemininingwane ehlukile yomuntu ofanayo, ngaphandle kwendlela ecacile yokuyiqaphela noma yokuyigwema.

Ukuhlukanisa leli tafula zibe amatafula amabili, Othisha nabaFundo (njengoba kuboniswe ngezansi), kudala ubudlelwane obufanele phakathi kwedatha futhi ngaleyo ndlela kusiza ukuqinisekisa ukuhambisana kwedatha nokuchithwa.