\begin{frame}[t]
  \frametitle{Cardinality Limits: Alternative Notations}

  \begin{alertblock}{}
    There are many different notations for ER models.
  \end{alertblock}
  \bigskip
  
  For example:  Chen style
  \begin{center}\vspace{-1.5ex}
    \includegraphics[width=.6\textwidth]{images/notation2.png}
    \vspace{-3ex}
  \end{center}
\end{frame}