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\begin{frame}
  \frametitle{ISA to Relational Model}

  \isaexample
  \begin{goal}{Method 3: one table with null values}
    From a single table with all local and specialised attributes.
  \end{goal}

  \begin{center}
  {\small\ttfamily
    \colorbox{rellight}{%
      \begin{tabular}[t]{|r|r|r|r|}
        \multicolumn{4}{c}{person}        \\ \hline
        \hd{id} & \hd{name} & \hd{salary} & \hd{credit-rating} \\ \hline 
        1 & James & 4000 & null  \\
        2 & Jones & null & 42 \\
        \hline
      \end{tabular}%
    }}
  \end{center}
  \pause
  
  \begin{itemize}
    \item advantage: no joins
    \item drawback: null values for entities that do not have the corresponding attribute  
  \end{itemize}
  \vspace{10cm}
\end{frame}