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\begin{frame}
  \frametitle{Foreign Key Constraints}
  
  \begin{alertblock}{}
    Once a foreign key is declared,
    the \emph{the following update update operations violate the foreign key constraint}: 
    \begin{itemize}
    \medskip
    \pause
      \item \emph{Insertion} into table \sql{RESULTS}\\ without matching tuple in \sql{STUDENTS}%
        \begin{itemize}
        \smallskip
    \pause
          \item DBMS \emph{rejects} the update
        \end{itemize}
    \medskip
    \pause
      \item \emph{Deletion} from  table \sql{STUDENTS} \\if the deleted tuple is referenced in \sql{RESULTS}
        \begin{itemize}
        \smallskip
    \pause
          \item DBMS \emph{rejects} the update, or
        \smallskip
    \pause
          \item deletion \emph{cascades}, that is, tuples in \sql{RESULTS}
            referencing the deleted tuple will also be deleted, or
        \smallskip
    \pause
          \item the foreign key is \emph{set to null} in \sql{RESULTS}.
        \end{itemize}
    \end{itemize}
  \end{alertblock}
\end{frame}