# Функциональные зависимости Нормализация отношений

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. . -. . . - . . . . R {A 1 , A 2 , A n } - PowerPoint PPT Presentation

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(.) & Co , 5999-99-99 3 & Co , 5999-99-99 5-., 1333-33-334 & Co , 5999-99-991 1444-44-442 & Co , 5999-99-993

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& Co , 5999-99-99-., 1333-33-33 1444-44-44

(.) & Co 3 & Co 5-4 & Co12 & Co3

• R {A1, A2, An}S {B1, B2, Bm}T {C1, C2, Ck}1) {A1, A2, An}= {B1, B2, Bm} {C1, C2, Ck}2) S= B1, B2, Bm (R)3) T= C1, C2, Ck (R)

• :, .. ( ); , ( ); .

• R {A1, A2, An}X, Y {A1, A2, An}X Y X YX Y |Y(X=x(R))|1 , . ,

• A1, A2, An B1, B2, Bm : {B1, B2, Bm } {A1, A2, An } {B1, B2, Bm } {A1, A2, An } {A1, A2, An } {B1, B2, Bm } {A1, A2, An } {B1, B2, Bm } =

• ,

F , R

AC , B, AB BC CA

• R {A1, A2, An}{B1, B2, Bm } {A1, A2, An }F - Z={B1, B2, Bm }+ Z0 := {B1, B2, Bm }BiBj CZ1:=Z0C{B1, B2, Bm } += {A1, A2, An } {B1, B2, Bm } -

• R {A, B, C, D, E, F} S = {AD, ABE, BFE, CDF, EC} {AE}+ ?

• R {A, B, C, D, E, F} S = {AD, ABE, BFE, CDF, EC} {AE}+ = ACDEF

• BA, AB ; AB, ACBC ; AB BC, AC .

• ( )1. XY XZ, XYZ. XY + 2 = XXY, XZ + A2 = YXYZ + A3 = XYZ2. XY WYZ, WXZ. XY +A2 = WXWY. WYZ + A3 = WXZ.3. XY ZY, XZ. 1 + 3.

• F+ - , F, F , , ,

• R {A1, A2, An}F - B1, B2, Bm C (B1, B2, Bm C) F+ , ifC{B1, B2, Bm }+

• :R (A, B, C, D)AB C, C D, DA ,

• F2 F1, , F1, F2.F1+F2+F1 F2 , F1+ = F2+.

• F ( ); F+; F F+.

• , , , . ., , r = R1(r) R2(r) ... Rn(r).

• ? Z(F): XY XYZ , F.

• 1 () . , .2 1 + , , , ., , , ,

• 3 : A, B, C , AB, BC, A B B C. , C A.3 2 , , .

• : , , ,

, ,

• : 3 (, , )2 , 3 (, , , ), , .

• - XA, AX, X R.(, , ) 3 , . (, ), (, ), , .

• -(, , ) 3 , . (, ), (, ), , .

• : , . 3 . .

• , X Y ( , Y). . X W, X Z XYWZ YWZ

• S G H R C T

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