AlgoPlus//structures / fds

Functional Dependencies

Compute an attribute set's closure to test whether it's a key.

Closure size

0/5

Step

1/1

Your FDs (e.g. A->BC, CD->E, B->D, E->A)

Starting attribute set (e.g. A or C, D)

Legend

In closure / applied FD

Just added

Not reached

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In a nutshell

A functional dependency is a rule saying one set of columns fixes the value of another: if you know X, you know Y. Starting from some columns and repeatedly applying every rule whose left side you already have gives the closure — the full list of columns those starting columns determine. If that closure grows to cover every column, the starting set can identify any row, so it's a key. Computing the closure is exactly how you test that.

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FD X→Y means X determines Y. Closure X⁺ — add the RHS of any FD whose LHS is already in the set — tells you everything X determines; if that is all attributes, X is a key.

Key terms

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Read the full theory, intuition & complexity for Functional Dependencies.