Dab tsi yog schema thiab Subschema hauv DBMS?
Dab tsi yog schema thiab Subschema hauv DBMS?

Video: Dab tsi yog schema thiab Subschema hauv DBMS?

Video: Dab tsi yog schema thiab Subschema hauv DBMS?
Video: Mus ua nyab rau yim hmoob tsis zoo 7/27/2017 2024, Kaum ib hlis
Anonim

A subschema yog ib tug subset ntawm cov schema thiab tau txais cov khoom qub qub uas a schema muaj. Txoj kev npaj (los yog tswvyim) rau kev pom feem ntau hu ua subschema . Subschema yog hais txog daim ntawv thov programmer's (tus neeg siv) saib ntawm cov ntaub ntawv yam khoom thiab cov ntaub ntawv hom, uas nws siv.

Tom qab ntawd, dab tsi yog schema hauv DBMS?

Lub database schema ntawm ib lub database yog nws cov qauv piav nyob rau hauv ib hom lus raug txhawb los ntawm database tswj system ( DBMS ). Lub sij hawm " schema " yog hais txog lub koom haum ntawm cov ntaub ntawv raws li daim ntawv qhia txog yuav ua li cas lub database yog tsim (sib faib rau hauv database tables nyob rau hauv cov ntaub ntawv ntawm relational databases).

Tsis tas li ntawd, qhov piv txwv database schema yog dab tsi? A schema muaj schema cov khoom, uas tuaj yeem yog cov ntxhuav, kab, cov ntaub ntawv hom, kev pom, cov txheej txheem khaws cia, kev sib raug zoo, cov yuam sij tseem ceeb, cov yuam sij txawv teb chaws, thiab lwm yam. schema daim duab sawv cev rau peb lub rooj me me database . Saum toj no yog ib qho yooj yim piv txwv ntawm a schema daim duab.

Yog li ntawd, Schema thiab Instance hauv DBMS yog dab tsi?

Cov Schema thiab Piv txwv yog cov ntsiab lus tseem ceeb ntsig txog databases. Qhov sib txawv loj ntawm schema thiab piv txwv nyob hauv lawv txhais qhov twg Schema yog cov lus piav qhia ntawm cov qauv ntawm database whereas Piv txwv yog cov txheej txheem ntawm cov ntaub ntawv tam sim no khaws cia rau hauv cov ntaub ntawv ntawm lub sijhawm tshwj xeeb.

3 hom schema yog dab tsi?

DBMS Schema Cov yog ntawm peb hom : Lub cev schema , logical schema thiab saib schema.

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