On Monday
On Monday
–
–
We
Started Looking at
We
Started Looking at
Relational Database Design
Relational Database Design
We looked at some example scenarios and saw that some
of them were not “good”
That motivated a desire to develop a theory to
Decide whether a particular relation
R
is in “good” form.
In the case that a relation
R
is not in “good” form, decompose
it into a set of relations {
R
1
, R
2
, ..., R
n
} such that
each relation is in good form
the decomposition is a lossless-join decomposition
theory is based on functional dependencies and multivalued
dependencies
First normal form
⇒
all attributes in a relation R are atomic
Definition of what it means for a functional dependency to
hold on a relation R
a functional dependency
α→β
holds on a relation schema R
iff for any legal relation r(R) with
α ⊆
R and
β ⊆
R,
t
1
[
α
] = t
1
[
α
]
⇒
t
2
[
β
] = t
2
[
β
]

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