: MVD
r (, ) A B MVD A B , A B, A UNION B r.
MVD . A B FD. A UNION B = Hr .
n- n > 2 __, {_, _, _} MVD. . 24.
. 24, __ __ __, , _. , .
2.3.10.2. /
, __ __, __ _ (, , __, __, __ _ ):
IF (<, > AND <, > AND <, > )
THEN <, , >
__ __, __ _ __, :
IF (<1, 1, 2> AND <2, 1, 1> AND <1, 2, 1> )
THEN <1, 1, 1>
, __ :
, , , .
/. .
r, A, B, , Z r (, ). r / (Project-Join Dependency PJD) *(A, B, , Z) , r A, B, , Z.
. 24. __ ( ),
|
|
2.3.10.3. , /
__ PJD* ({_, _}, {_, _}, {_, _}). PJD , , ? __? : . , __ , . 25.
. 1 (. 25) <2941, 1, A>, <2934, 1, A>. , <2934, 1, B>, <2941, 1, A> <2934, 2, A>. <2934, 1, A>. , <2934, 1, A> , , <2941, 1, A>.
. 2 <2934, 1, A>, <2941, 1, A>, . , <2941, 1, A> .
. 25. __