\begin{frame}
  \frametitle{Other Constraints}
  
  \begin{exampleblock}{Multiple choice test}
  The following relation stores the solutions to a typical
  multiple choice test:

  \centering\footnotesize\ttfamily
  \colorbox{rellight}{%
    \begin{tabular}{|r|r|r|r|}
      \multicolumn{4}{c}{Answers}
      \\
      \hline
      \hd{\underline{question}} & \hd{\underline{answer}} & \hd{text}
      & \hd{correct} 
      \\
      \hline
      1 & a & ... & Y \\
      1 & b & ... & N \\
      1 & c & ... & N \\
      2 & a & ... & N \\
      2 & b & ... & Y \\
      2 & c & ... & N \\
      \hline
    \end{tabular}%
  }
  \end{exampleblock}
  \medskip
  
  \begin{quiz}{\textwidth}{Using keys to enforce other constraints}
    The following is not an FD, MVD, or JD:
    \begin{tcenter}
      ``\textit{Each question can only have one correct answer.}''
    \end{tcenter}
    Can you suggest a transformation of table \sql{Answers} such
    that the above constraint is already implied by a key?
  \end{quiz}
  %% Split ANSWERS vertically into 
  %%    CORRECT_ANSWERS(QUESTION,ANSWER,TEXT)   key: QUESTION
  %% and
  %%    WRONG_ANSWERS(QUESTION,ANSWER,TEXT)     key: QUESTION,ANSWER
  %%
  %% The key in CORRECT_ANSWERS ensures that only one entry is made for
  %% each question (multiple wrong answers may be recorded in
  %% WRONG_ANSWERS).
  %%
  %% New inter-relational constraint needed: same question with same
  %% answer may not appear in both tables
\end{frame}