. 6. _
. 6. _
. 6. , (1) , , . , , , . , , ?
, . , _ _ _. (1) , _ , _. , ( ) _, _, _ . _, , . 7.
, ( ), _, , . , , _ _ _ _ _, .
1 :
.
r {A, B, C} (A, B C, , ) FD A B.
. 7. _
r = (r PROJECT {A, B}) NATURAL JOIN (r PROJECT {A, C}).
__ {_, _, _} (. 8). _ , , _ , . , . . FD _ _, .
. 8.
__ _ , , . 8, FD _ _ .