Functional Dependency

Goals

Our goals of database design with functional dependencies are:

1. BCNF.
2. Losslessness.
3. 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.

Links

• Normal Form
• Armstrong Axiom
• Canonical Cover
• Lossless Decomposition
• Extraneous
• data structures - Find candidate keys given functional dependencies - Computer Science Stack Exchange