Video: Dab tsi yog qhov sib tshooj subtype?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Overlapping subtypes yog subtypes uas muaj cov tsis tshwj xeeb subsets ntawm lub supertype chaw teeb; uas yog, txhua qhov chaw piv txwv ntawm tus supertype yuav tshwm sim hauv ntau dua ib qho subtype . Piv txwv li, nyob rau hauv ib cheeb tsam tsev kawm ntawv, ib tug neeg tej zaum yuav yog ib tug neeg ua hauj lwm los yog ib tug me nyuam kawm ntawv los yog ob qho tib si.
Tom qab ntawd, ib tug kuj yuav nug, dab tsi yog overlapping nyob rau hauv database?
Kev sib tshooj subtype: Tsis yog tshwj xeeb subsets ntawm lub supertype entity set yog hu ua sib tshooj subtype. Txhua qhov chaw piv txwv ntawm supertype tuaj yeem tshwm sim tsawg kawg ib hom subtype. Txoj cai no tau teev nrog tsab ntawv "o" hauv lub voj voog yog txuas ntawm tus supertype thiab nws cov subtypes.
Ib yam li ntawd, dab tsi yog disjoint subtype? Disjoint subtypes , tseem hu ua nonoverlapping subtypes , yog subtypes uas muaj ib tug tshwj xeeb subset ntawm lub supertype chaw teeb; Hauv lwm lo lus, txhua qhov chaw piv txwv ntawm supertype tuaj yeem tshwm sim hauv ib qho ntawm cov subtypes.
Hais txog qhov no, lub hom phiaj ntawm ib tug subtype discriminator yog dab tsi?
A subtype discriminator yog tus cwj pwm nyob rau hauv qhov chaw supertype uas yog siv los txiav txim seb qhov chaw twg subtypethe supertype tshwm sim cuam tshuam. Rau txhua qhov muab supertype tshwm sim, tus nqi ntawm tus subtype discriminator yuav txiav txim qhov twg subtype qhov tshwm sim supertype muaj feem xyuam nrog.
Qhov txawv ntawm ib nrab tiav thiab tag nrho cov tiav yog dab tsi?
Ib nrab ua tiav txhais tau hais tias qee qhov tshwm sim supertypes yuav tsis yog cov tswv cuab ntawm ib qho subtype. Tag nrho ua tiav txhais tau hais tias txhua qhov tshwm sim supertype yuav tsum yog ib tus tswv cuab ntawm tsawg kawg ib hom subtype.
Pom zoo:
Dab tsi yog qhov kev txwv sib tshooj?
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