????? ????? (Design Theory) - PowerPoint PPT Presentation

About This Presentation

Title:

????? ????? (Design Theory)

Description:

for each subset X of R with i attributes. if closure(X,F)=R. Return X. ???? ?????? ???'? ... While there is an attribute A. such that F = K-{A} A K := K {A} ... – PowerPoint PPT presentation

Number of Views:15

Avg rating:3.0/5.0

Slides: 29

Provided by: csHu

Category:

more less

Transcript and Presenter's Notes

Title: ????? ????? (Design Theory)

1
????? ????? (Design Theory)

???? ??????

2
???? ?? ????? ??????????

??? R ????? ??????????, F ????? ??????
????????????
????? ?? X ????? X ????? ?? ?? ??????????? ?-R
??????? ?-X
X A F X?A

??? ???? ???? ???? ?? ????? ???????????
??? ???? ?????? ?- ? ?
3
?????

RABCDE
FAB?C, CE?B, D?A, BC?E
A
A,B
B,D

4
???????? ????? ?????? ????

Compute Closure(X,F)
Set C X
While there is a V?W in F such that V ? C and W ?
C
C C ? W
Return C

5
???????? ??? ????

???????? ??? ???? O( X2F )
???? ????????? ??? ??? ????? ????? ??????????? ?-
X
??? ??????? ?????? ??? ????? F ??????
?? ????? ??? ???? ?-C ??? ????? ???? ??????????
?-X

6
???????? ???? ????

?????? ???? ??? ???? ??? ?"? ?? F ?????? ???
???????? ?? R
??????? ????? ????? ?? ???? (size) ?????? ???
(tail)
???? ?? ???? X?Y, ????? ?? ??"? ??????
true ??? ??????? ??? ?????????? ?- X
?? ???? ??????????? ?-X ?????? size
?? Y ?????? tail

7
???? ?????
F A ? C, B ? D, AD ? E
A B C D E Size Tail
A ? C ? 1 C
B ? D ? 1 D
AD ? E ? ? 2 E
8
Compute Closure(X, F, T) / T is the table
/ C X Q X While Q is not empty A
Q.dequeue() for i1..F if Ti,Atrue then
Ti,size Ti,size1 if Ti,size0,
then Q Q ? (Ti,tail\C) C C ? Ti,tail
9
????? AB
Start X A,B, Q A, B
A B C D E Size Tail
A ? C ? 1 C
B ? D ? 1 D
AD ? E ? ? 2 E
10
????? AB
Iteration of A X A,B,C, Q B,C
A B C D E Size Tail
A ? C ? 0 C
B ? D ? 1 D
AD ? E ? ? 1 E
11
????? AB
Iteration of B X A,B,C,D, Q C,D
A B C D E Size Tail
A ? C ? 0 C
B ? D ? 0 D
AD ? E ? ? 1 E
12
????? AB
Iteration of C X A,B,C,D, Q D
A B C D E Size Tail
A ? C ? 0 C
B ? D ? 0 D
AD ? E ? ? 1 E
13
????? AB
Iteration of D X A,B,C,D,E, Q E
A B C D E Size Tail
A ? C ? 0 C
B ? D ? 0 D
AD ? E ? ? 0 E
14
????? AB
Iteration of E X A,B,C,D,E, Q
A B C D E Size Tail
A ? C ? 0 C
B ? D ? 0 D
AD ? E ? ? 0 E
15
????????

???????, ???? ??? ????? ??? ?? ?????? true ?????
??? ??? ????? ????? ?????? true

A B C D E Size Tail
A ? C ? 1 C
B ? D ? 1 D
AD ? E ? ? 2 E
16
???????? ??? ????

?????? ???? ?- O( F X )
?????? ?? ?? ??????????? ?? X
???? ???????? ?????? ????? ??? ??? ????? ?????
??????????? ???????? ??? ???? ?? ???? ?-F
??? ????????? ?????

17
????? ????

????? ????? R ?????? ?????? ???????????? F
????? ????? ???? (?????) ???? R
???????? ?????
?????? ?? ?? ?? ??????? ?? ?????????? ?-R ???
???????? ?????? ????? ??????? ?????? ??????
??????? ???? ?????? ????? ?????? ??? ??? R
??? ????????? ?????

18
?????????

Compute Key(R, F)
for i1 to R
for each subset X of R with i attributes
if closure(X,F)R
Return X

19
???????? ???????

?? ?-R ?? n ?????????? ?? ?? n!/(n-i)!i!
???????? ?????? ?????? ????? i ?-R ????? ??
?????? ????? ????
????? ???????? ???? ????
?????? ?????? "??????"

20
????? ????
Compute Key(R, F) Set K R While there is an
attribute A such that F ? K-A?A K K
\A Return K
21
?????

RABCDE
FAB?C, CE?B, D?A, BC?E
?????? KABCDE
???? D?A ?????? KBCDE
???? CE?B ?????? KCDE
?? ???? ?????? ??? ?????????? ???? ??? ????

22
??? ????

?????? ???? ??? ????? R ????? ???? ??? ?????
O(RF)
???? ????????? ?????

23
????? ?????? ?????

RABCDE
FABC?D, D?B, B?C, AD?BC
????? ????? ???? ??????, ???? ???? ?????? ???????
????? ??? ?????

24
????? ??????

????? ????? ??? ????????
????? ?? ???????
????? ???? ???????
????? ?????
????? ????? ???????? ?? ??????

25
?????? ?????? ????? ??? ????????
????? ???? ?- ???? ??? ?????
????? ?????? ??????? ???? ?????? ????? ???? ????
???? ?????? ??????? ???? ?????? ????? ???? ???? ????? ??? ????
26
?????