\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{\ul{id}} & \hd{name} & \hd{salary} & \hd{credit-rating} \\ \hline 
        1 & James & 4000 & null  \\
        2 & Jones & null & 42 \\
        \hline
      \end{tabular}%
    }}
  \end{center}
  \pause\bigskip
  
  \textbf{Advantage:} no joins\\[.5ex]
  \textbf{Drawback:} null values for non-applicable attributes\\
  \remark{For instance, salary will be null for customers.}
  \vspace{10cm}
\end{frame}