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Video: Ib qho piv txwv ntawm qhov chaw tsis muaj zog yog dab tsi?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
A tsis muaj zog qhov chaw yog ib qho uas tsuas muaj nyob tau thaum muaj lwm tus. Rau piv txwv : ROOM tsuas tuaj yeem muaj nyob hauv BUILDING. Ntawm qhov tod tes, TIRE tej zaum yuav suav tau tias muaj zog qhov chaw vim nws tseem tuaj yeem nyob tsis tau txuas nrog CAR.
Tsis tas li ntawd, dab tsi yog txhais los ntawm qhov chaw tsis muaj zog?
Nyob rau hauv kev sib raug zoo database, a tsis muaj zog qhov chaw yog ib qhov chaw uas tsis tuaj yeem raug txheeb xyuas los ntawm nws cov attributesalone; yog li ntawd, nws yuav tsum siv tus yuam sij txawv teb chaws ua ke nrog nws cov cwj pwm los tsim tus yuam sij tseem ceeb. Tus yuam sij txawv teb chaws feem ntau yog qhov tseem ceeb ntawm tus yuam sij qhov chaw nws muaj feem rau.
Tsis tas li ntawd, dab tsi yog qhov chaw muaj zog thiab tsis muaj zog? Cov qhov chaw teeb uas tsis muaj txaus attributes los tsim ib tug thawj key yog hu ua Qhov chaw tsis muaj zog teeb. Ib qhov chaw teeb uas muaj qhov tseem ceeb yog hu ua Qhov chaw muaj zog teeb. Kev ntxub ntxaug ntawm a tsis muaj zog qhov chaw teeb yog ib txheej ntawm cov cwj pwm uas tso cai rau qhov kev sib txawv no bemade.
Ib yam li ntawd, qhov piv txwv muaj zog yog dab tsi?
Strong Entity Nws lub neej tsis yog nyob ntawm lwm tus qhov chaw . Strong Entity yog sawv cev los ntawm ib daim duab plaub: txuas ntxiv peb yav dhau los piv txwv , xibfwb yog a lub koom haum muaj zog ntawm no, thiab tus yuam sij tseem ceeb yogProfessor_ID.
Cov koom haum yog dab tsi?
Hom Lub Npe –
- Hom Lub Hom Phiaj.
- Recursive Entity Types.
- Yam Tsis Muaj Chaw.
- Composite Entity Types lossis Associative Entity Types.
- SuperType thiab SubType Entities.
Pom zoo:
Ib qho chaw tsis muaj zog puas tuaj yeem muaj qhov chaw tsis muaj zog?
Hom chaw tsis muaj zog muaj qee qhov yuam sij. Nco tseg- Lub koom haum tsis muaj zog ib txwm muaj kev koom tes tag nrho tab sis lub koomhaum muaj zog yuav tsis muaj tag nrho kev koom tes.Weak entity yog nyob ntawm qhov chaw muaj zog kom ntseeg tau tias muaj qhov tsis muaj zog. Zoo li lub koom haum muaj zog, qhov tsis muaj zog tsis muaj qhov tseem ceeb, Nws muaj feem cuam tshuam kev ntxub ntxaug
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