Multivalued Dependencies 4 C5 c) \! l' wFourth Normal Form" L6 e: _. V) J3 M1 x- i& d9 V(欢迎访问avcar:https://avcar.vip)
Reasoning About FD’s + MVD’s) n+ @0 O! u0 c2 J8 b+ E(欢迎访问avcar:https://avcar.vip)
1 + C. W& V" N; h" E( JDefinition of MVD9 K w6 d" p1 E) Y( @0 Y2 R3 K(欢迎访问avcar:https://avcar.vip)
A multivalued dependency (MVD) on ) w3 b8 h H1 J8 a: l! ER, X ->->Y , says that if two tuples of R' w4 R: ], W6 f! p( ? S(欢迎访问avcar:https://avcar.vip)
agree on all the attributes of X, then ! O4 j6 r- j" ^8 E0 Htheir components in Y may be 8 w2 L7 E( E+ Y$ M; o$ U(欢迎访问avcar:https://avcar.vip)
swapped, and the result will be two 9 B# v7 j0 I8 Ktuples that are also in the relation. 7 V9 g8 a, g( E, T3 Zi.e., for each value of X, the values of Y % |* L1 U% e3 p3 Sare independent of the values of R-X-Y. 2; ^. X: O/ G/ m+ _/ z& v(欢迎访问avcar:https://avcar.vip)
3 3 u$ a8 i) Q; J$ m- y0 R# uExample: MVD9 E" r3 @3 |6 h9 V8 R(欢迎访问avcar:https://avcar.vip)
Drinkers(name, addr, phones, beersLiked) ( V& u0 v0 i( n0 c3 QA drinker’s phones are independent of * L0 U/ D6 n. _/ m; v(欢迎访问avcar:https://avcar.vip)
the beers they like. " L. `, W( i$ qname->->phones and name ->-; [! `$ c' i1 d* b# X4 L(欢迎访问avcar:https://avcar.vip)
>beersLiked.' f$ i3 G1 j: l, m# P9 P3 j t* O# a(欢迎访问avcar:https://avcar.vip)
Thus, each of a drinker’s phones appears ) s, ^, c, `7 ?. z3 b1 a5 X+ y1 Vwith each of the beers they like in all 6 L' l- m7 e# i(欢迎访问avcar:https://avcar.vip)
combinations. ( G: x. b: m4 p# D( c' K2 o% \This repetition is unlike FD redundancy.: N. a- c( V" E! N8 Q3 r9 X: G(欢迎访问avcar:https://avcar.vip)
name->addr is the only FD., o$ N, Y' ]; C(欢迎访问avcar:https://avcar.vip)
48 l9 }+ A/ x" P$ O1 v6 M. J(欢迎访问avcar:https://avcar.vip)
Tuples Implied by name->->phones ' m1 @. ^0 X" ~9 d5 G* z" cIf we have tuples: " b6 Y+ X, B* f5 Aname addr phones beersLiked1 m" [, H, d4 d0 t(欢迎访问avcar:https://avcar.vip)
sue a p1 b19 F ^, C; _* H/ ]( Y# z8 U+ }(欢迎访问avcar:https://avcar.vip)
sue a p2 b2 & `! L% _8 [0 J* L* @" C5 `2 Q0 @) Asue a p2 b1" E- K! M! g @8 [(欢迎访问avcar:https://avcar.vip)
sue a p1 b27 c( Q) l" a: G1 v- @/ n) f(欢迎访问avcar:https://avcar.vip)
Then these tuples must also be in the relation.( U& d. D3 v) v( J. t8 t(欢迎访问avcar:https://avcar.vip)
5 0 b/ H7 V3 P6 ^* [' ?: L- tPicture of MVD X ->->Y X Y others , T' T" B2 w; t- b' _( U5 M7 i; Hequal# ~# E( M, u: s9 `1 X& D(欢迎访问avcar:https://avcar.vip)
exchange