Normalization ntawm databases

Grouping ntawm tib cov ntaub ntawv nyob rau hauv lub rooj tau nyob rau hauv ntau txoj kev. Tej cwj pwm nyob rau hauv ib tug kev sib raug zoo yuav tsum tau grouped raws li lub hauv paus ntsiab lus paub, uas yog, nws yuav tsum tau tag nrho txo luam ntawm cov ntaub ntawv, raws li tau zoo raws li simplifying tus txheej txheem rau lawv kev kho mob raws li los ntawm ib qho hloov tshiab. Ib tug ntawm cov thawj muaj teeb meem nrog tsim database ua tshem tawm ntawm redundancy, thiab nws yog tiav los ntawm normalization.

Normalization database nruab nrab yog ib tug formal apparatus txwv los tsim lub rooj uas tso cai rau los mus tshem tawm Individuals, nrog lub taub hau yuav tsum tau software muab ntaub ntawv, kom txhob muaj cov ua hauj lwm rau cov nqi uas txuam nrog kev tswj thiab database txij nkawm. Normalization lag luam muaj nyob rau hauv lub expansion ntawm tus thawj database ntxhuav rau hauv yooj yim. Nyob rau txhua theem ntawm txoj kev no tas rooj muab nyob rau hauv lub cev daim ntawv. Txhua theem yog yus muaj los ntawm normalization ntawm ib tug tej yam txheej txwv, uas yuav tsum tau ua raws li nrog tag nrho cov rooj. Yog li, qhov kev tshem tawm yog nqa tawm uas tsis yog-tseem ceeb cov lus qhia, uas yog redundant.

Normalization ntawm databases yog raws li nyob rau hauv lub tswv yim ntawm kev haumxeeb quav ntawm tej cwj pwm. Nws yog suav tias yog hais tias ib tug cwj pwm yog nyob rau ntawm lwm yam, yog tias txhua lub sij hawm ib tug nqi ntawm lub thib ob attribute sau raws nkaus Ii tsis muaj ntau tshaj li ib tug ntawm cov thawj nqis.

Normalization ntawm databases - ib lub sij hawm, li cas los xij, nws yuav subdivided rau hauv ob peb ib txwm cov ntaub ntawv, uas yuav tsum tau los sib tham tom qab.

Ib tug cov ntaub ntawv kwv yog xam tau tias yog cov mus rau tus thawj ib txwm daim ntawv thaum tus nqi ntawm txhua tus cwj pwm yog nws ib. Yog hais tias ib tug tej yam cwj pwm muaj ib tug duplicate nqi, nws yuav tsis muab suav hais tias ib tug kwv teej tug mus rau tus thawj ib txwm daim ntawv. Nws hloov tawm hais tias koj muaj peev xwm tsim ib tug tseem tej qhov chaw uas yog ib tug cov ntaub ntawv kwv.

Ib tug cov ntaub ntawv kwv yog pom tau hais tias yuav mus rau lub thib ob ib txwm daim ntawv thaum nws yog twb nyob rau hauv thawj ib txwm daim ntawv no, tab sis txhua tus ntawm nws cov cwj pwm, tsis muaj nyob rau hauv ib tug tej zaum yam, kiag ywj siab nyob rau hauv haumxeeb cov nqe lus los ntawm txhua tus lub peev xwm tuav.

Ib tug cov ntaub ntawv kwv yog pom tau hais tias yuav mus rau lub thib peb ib txwm daim ntawv no, yog hais tias nws twb yog nyob rau hauv ob ib txwm daim ntawv no, tab sis nws tsis muaj tej transitive dependencies uas tsis yog-tseem ceeb cov khoom los ntawm cov lag luam. Nyob rau hauv lub transitive quav yog feem ntau to taub raws li ib qho cuab kev sib raug zoo ntawm lub teb.

Normalization database txo nws hwj tus tsim tawm hom phiaj tseem ceeb coj tag nrho kev sib raug zoo mus rau lub thib peb ib txwm daim ntawv. Tsuas yog nyob rau hauv no txoj kev nyob rau hauv lub neej yav tom ntej nws yuav tau los mus tsim ib tug npaum ntaub ntawv system.

Normalization ntawm databases: kev cai

Nws yuav tsum npaj ib tug txheej ntawm cov kev cai yuav tsum tau ua raws li nyob rau hauv lub chaw ua hauj lwm ntawm normalization. Tus thawj yog mus cais cov rov qab ua dua pawg. Tsim nyog mus ua ib lub cais rooj khaws cia txhua set ntawm lwm yam kev cwj pwm, uas tsim ib tug nyias muaj nyias ib qhov tseem ceeb. Tom ntej no, nco ntsoov tshem tawm redundant cov ntaub ntawv. Nyob rau hauv tus neeg mob qhov twg lub attribute kev sib raug zoo yog cai xwb nyob rau ib feem ntawm tus yuam sij, ces nws yuav tsum tau muab tso rau hauv ib tug nyias muaj nyias ib lub rooj. Qhov thib peb txoj cai yog yuav tsum tau tsuas yog rau txhua uas tsis yog nyob ntawm seb qhov tseem ceeb. Tej cwj pwm yuav tsum tau muab tso rau hauv ib tug raug rho tawm rooj, yog hais tias lawv tsis muaj lub xav ntxim rau cov qhov tseem ceeb. Nco ntsoov cais tawm lub ywj siab ntau yam kev sib raug zoo. Nyob rau hauv cov ntaub ntawv no peb yuav sib tham txog dab tsi yog tsis tau pom pob zeb ua kev twb kev txuas ntawm ntau yam kev sib raug zoo. Thaum kawg, nws yog tsim nyog los cais lub ntau yam kev sib raug zoo hais txog semantically. Nyob rau hauv no database normalization tiav, ua raws li los ntawm ib tug kev loj hlob.