2.5 .
, , . .
1. .
2. () ( ). , .
3. , .
4. , (, , ).
5. . , - "" , . , = 2 "" . 3.2 = 7 ( ), , "" , 2, 7.
6. . , (, "" 12 ).
60- , , .. . IBM - . (Codd E.F., A Relational Model of Data for Large Shared Data Banks. CACM 13: 6, June 1970), , , " ".
. (, , , ). , , relation (.).
() . , , , .
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. , , , , (, " , "). , , , : ?
D1, D2,..., Dn ( , ) .
, - (Ai:Vi), (i=1,2,...,n), Ai . - (Ai:Vi) Vi Di, Ai.
. , , ,..., n n-. "" - 8.
. "" 10. .
, , - . R A1, A2,..., An. , K=(Ai, Aj,..., Ak) R R , :
1. : R Ai, Aj,..., Ak.
2. : Ai, Aj,..., Ak K .
, . ( ) . , , .
, , , .