Video: Functional Dependency piav qhia luv luv yog dab tsi?
2024 Tus sau: Lynn Donovan | [email protected]. Kawg hloov kho: 2023-12-15 23:47
Functional dependency yog kev sib raug zoo uas tshwm sim thaum ib tus cwj pwm tshwj xeeb txiav txim siab lwm tus cwj pwm. Yog tias R yog kev sib raug zoo nrog tus cwj pwm X thiab Y, a functional dependency nruab nrab tus tus cwj pwm yog sawv cev li X->Y, uas qhia tias Y yog functionally nyob ntawm X.
Tib neeg kuj nug, dab tsi yog qhov kev vam khom ua haujlwm piav qhia nws nrog piv txwv?
Functional dependency hauv DBMS. Cov cwj pwm ntawm lub rooj tau hais tias yog nyob ntawm ib leeg thaum tus cwj pwm ntawm lub rooj tshwj xeeb txheeb xyuas lwm tus cwj pwm ntawm tib lub rooj. Rau piv txwv : Piv txwv tias peb muaj ib lub rooj tub ntxhais kawm nrog cov cwj pwm: Stu_Id, Stu_Name, Stu_Age.
Tsis tas li ntawd, qhov kev siv ntawm kev ua haujlwm nyob hauv DBMS yog dab tsi? Functional dependencies yog siv nyob rau hauv tus tsim (los yog redesign) ntawm relational databases los pab tshem tawm redundancy (cov ntaub ntawv duplication), yog li ntawd yuav txo tau cov kev hloov tshiab anomalies. Redundancy raug tshem tawm los ntawm tus txheej txheem hu ua normalization.
Raws li txoj cai, kev ua haujlwm ntawm kev vam thiab nws hom yog dab tsi?
Cov ntsiab lus. Functional Dependency yog thaum ib tus cwj pwm txiav txim siab lwm tus cwj pwm hauv DBMS system. Axiom, Decomposition, Dependent, Determinant, Union yog cov ntsiab lus tseem ceeb rau functional dependency . Plaub hom ntawm functional dependency yog 1) Multivalued 2) Trivial 3) Non-trivial 4) Transitive.
Vim li cas peb thiaj xav tau kev vam khom?
Functional dependencies yog siv los tsim kev sib raug zoo nyob rau hauv Boyce Codd Normal Form abbreviated li BCNF. Yog li functional dependency yog national_id -> npe; Functional dependency qhov tseem ceeb: Functional dependency yog ib qho tseem ceeb hauv kev sib raug zoo database tsim rau lub hom phiaj ntawm kev tshem tawm redundancy.
Pom zoo:
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