\begin{frame} \frametitle{Queries in Databases: Relational Model} \begin{exampleblock}{} \begin{center} \tablepersons \end{center} \end{exampleblock} \smallskip \pause \begin{goal}{Relational Model} The table is modelled by a ternary predicate \textit{Person}: \begin{talign} \text{\textit{Person}(101, Ann, Amsterdam)} \end{talign} Likewise, the predicate holds for every row of the table. \end{goal} \pause We can formulate \emph{queries using free variables}. \begin{exampleblock}{} The names of people living in Amsterdam: \pause \begin{talign} \{\; y \;\mid\; \myex{i}{\text{\textit{Person}}(i,y,\text{Amsterdam})} \; \} \mpause[1]{ \;\;=\;\; \{\;\text{Ann},\; \text{Mia}\;\} } \end{talign} \end{exampleblock} \end{frame}