In the relational model, relations are sets of tuples (similar to \glspl{record}). They are denoted $R(f_1: D_1, \ldots, f_n: D_n)$,
or sometimes simply $R(D_1, \ldots, D_n)$.
An \bi{instance} is a \bi{set} of tuples $I_R \subseteq D_1 \times \ldots \times D_n$.

\inlineintuition You can think of the instance to be the rows in the table.

\shade{orange}{Important} We define relations as \bi{mathematical sets}. This means that they cannot contain duplicates and the order does not matter.
Database engines may elect to do this differently, but this course assumes set semantics for the relational model.
