Tus nqi ntawm qhov nyuaj uas lub kaw lus tau saib lossis programmed. Cov qib siab dua, qhov nthuav dav tsawg. Qhov qis dua, qhov nthuav dav dua. Qhov siab tshaj plaws ntawm abstraction yog tag nrho cov system.
Dab tsi yog 4 theem ntawm abstraction?
Lub ANSI/SPARC architecture yog tsim los ntawm plaub theem ntawm cov ntaub ntawv abstraction; cov theem no yog external, tswvyim, sab hauv, thiab lub cev.
Dab tsi yog ob theem ntawm abstraction?
Physical level: Qib qis tshaj ntawm abstraction piav qhia tias lub kaw lus tau khaws cov ntaub ntawv li cas. Lub cev theem piav qhia cov txheej txheem cov ntaub ntawv qis qis hauv kev nthuav dav. Qib logical: qib siab dua ntawm kev paub daws teeb meem piav qhia txog cov ntaub ntawv twg hauv cov ntaub ntawv khaws cia, thiab kev sib raug zoo ntawm cov ntaub ntawv no.
Nws yog ib theem ntawm abstraction nyob rau hauv ib txoj kev xav?
Muaj peb theem uas peb tuaj yeem sib tham txog yam: khoom, kev paub thiab lub tswv yim. Raws li peb nce qib ntawm abstraction, cov tswv yim nce thiab kev muaj tiag rov qab.
3 theem ntawm cov ntaub ntawv abstraction yog dab tsi?
Summary
- Muaj peb theem ntawm cov ntaub ntawv abstraction: Internal Level, Conceptual or Logical Level or External or View level.
- Lub tswv yim sab hauv txhais cov qauv khaws cia ntawm lub cev.
- Lub tswv yim schema piav qhia cov qauv Database ntawm tag nrho cov ntaub ntawv rau cov zej zog ntawm cov neeg siv.
