\begin{frame} \frametitle{Non-Monotonic Behaviour} In natural language, queries that contain formulations like \begin{align*} & \begin{aligned} & \text{``\emph{there is no}''} \\ & \text{``\emph{does not exists}''} \end{aligned} && \Bigg\} && \begin{aligned} & \text{\emph{negated existential}} \\[-.7ex] & \text{\emph{quantification}} \end{aligned} \\[1ex] & \begin{aligned} & \text{``\emph{for all}''} \\ & \text{``\emph{the minimum/maximum}''} \end{aligned} && \Bigg\} && \emph{universally quantification} \end{align*} indicate non-monotonic behaviour. \pause\bigskip \begin{goal}{} In an equivalent SQL formulation of such queries, this boils down to a \emph{test whether a query yields a (non-)empty result.} \end{goal} \end{frame}