Functional Dependency
# Goals
Our goals of database design with functional dependencies are:
- BCNF.
- Losslessness.
- Dependency preservation
# Definition:
find a = find b, $\alpha \to \beta$,
In general, a functional dependency of the form α → β is trivial if β ⊆ α
# Trivial
if $\beta$ is a subset of $\alpha$
# 部分函数依赖
对子集函数依赖
# Closure
We shall use the notation $F^+$ to denote the closure of the set F, that is, the set of all functional dependencies that can be inferred given the set F. $F^+$ contains all of the functional dependencies in F.