红米手机额我哦明明地址
三生三世三生三世说的对对对
Multivalued Dependencies
Fourth Normal Form
Reasoning About FD’s + MVD’s
1
Definition of MVD
A multivalued dependency (MVD) on
R, X ->->Y , says that if two tuples of R
agree on all the attributes of X, then
their components in Y may be
swapped, and the result will be two
tuples that are also in the relation.
i.e., for each value of X, the values of Y
are independent of the values of R-X-Y. 2
3
Example: MVD
Drinkers(name, addr, phones, beersLiked)
A drinker’s phones are independent of
the beers they like.
name->->phones and name ->-
>beersLiked.
Thus, each of a drinker’s phones appears
with each of the beers they like in all
combinations.
This repetition is unlike FD redundancy.
name->addr is the only FD.
4
Tuples Implied by name->->phones
If we have tuples:
name addr phones beersLiked
sue a p1 b1
sue a p2 b2
sue a p2 b1
sue a p1 b2
Then these tuples must also be in the relation.
5
Picture of MVD X ->->Y X Y others
equal
exchange
djxjdn
大大大
范若若若若
vhh不会滚滚滚姐姐
，如果您要查看本帖隐藏内容请回复
来啦来啦
evevrbrb