Keys

Superkey

Given a relation $R$ with Attributes $\{A_1,...,A_k\}$ and subset $K$ of $R$, then $K$ is a superkey of $R$ if the FD $K\to R$ holds on any instance of $R$

Candidate Key

Given a relation $R$ with attributes $\{A_1,\dots ,A_k\}$ and subset $K$ of $R$, then $K$ is a candidate key of $R$, and no strict subset of $K$ is a superkey

• Can’t remove any attribute from a candidate key and still have a superkey

Primary Key

Given a relation $R$ with attributes $\{A_1,\dots ,A_k\}$, the primary key of $R$ is a distinguished candidate key of $R$ chosen by the DBA group