, , . . Branch 6 , . , , , .
( (intension)). , . (extension), (state) , .
, .
Branch (. . 1) , , . , 6- , .. , . 1 (unary) ( 1- ). (binary), (ternary), n - (n -ary). .
. . . , , .
. , , (normalization).
. , , , . (file), (records), (fields). , . . 3 , .
3
. , D 1 D 2, D 1 = {2,4} D 2 = {1,3,5}. ( D 1 x D 2) , D 1, D 2. , D 1, D 2. :
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D 1 D 2= {(2,1),(2,3),(2,5),(4,1),(4,3),(4,5)}.
. , R:
R = ((2,1),(4,1)}.
, , . , , R , 1, R :
R = {(x,y) | x D 1, y D 2, = 1}.
S, . S :
S = {(x, y) | x D 1, y D 2, = 2 }.
: S = {(2,1)}.
. : D 1, D 2 D 3. D 1 x D 2 x D 3 , , D 1, D 2, D 3. . :
D 1= {(1,3)}, D 2= = {(2,4)}, D 3= {(5,6)},
D 1 D 2x D 3= {(1,2,5), (1,2,6), (1,4,5), (1,4,6), (3,2,5), (3,2,6), (3,4,5), (3,4,6)}.
. , n . n D 1, D 2,.., Dn. n. :
D 1x D 2 x.x Dn = {(d 1, d 2,..., dn) | d 1 D 1, d 2 D 2,..., dnDn.
:.
n - n . , , , .
, . , . , 1, 2,..., n D 1, D 2,..., Dn { A 1: D 1, A 2: D 2,..., An: Dn }. R, S, . , R n - { A 1: d 1, A 2: d 2,..., An: dn }, d 1 D 1, d 2 D 2,..., dnDn.
n - . , (d 1, d 2,..., dn), . , , .
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, , Branch Bno, Street, City, Postcode, Tel_No Fax_No . Branch 6- , BRANCH_NUMBER, STREET_NAME .. , 6- :
{(23, , 111111, , 1231112, 1231113)}.
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{(Bno: 23, City: , Postcode: 111111, Street: , Tel_: 1231112, Fax _: 1231113)}
Branch 6- , . , .