. , __ : __ {_, _}, _ {_, _} __ {_, _}. __ 1 . 26.
. 26.
2941, A 1, , , <2941, 1> -_, <2941, A> - <1, A> _-. . 26.
, 2941, A 1, - __ 2 ( . 26). , .
.
__, _ __ , , , .
r PJD *(A, B, , Z) , A, B, , Z r, . . r.
r / *(A, B, , Z) , A, B, , Z r.
, PJD, , , , . , __ _ , , , PJD *({_, _}, {_, _}) ( ). / , . .
r , / (5NF, PJ/NF Project-Join Normal Form) , PJD r r.
, , r 5NF, r PJD . , . 4NF, , 4NF, , 5NF. ?
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, 5NF "" , . "" , , 5NF, , . , .
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;
.
, , , , . .
-, 20 . , , .
-, (On-Line Transaction Processing OLTP). 1 , . OLTP , , , .
(On-Line Analytical Processing OLAP). , , , , , , .
, ? !
. - , , . OLTP , . , - . , .
, OLAP, , (Decision Support System DSS). , , . , -, OLAP ( DataWarehouse), -, OLTP. OLTP- , .
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, OLAP-? ! , . , , .
. , , , . , "" , CASE-, .
2.4. : ER-