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\begin{frame}
  \frametitle{ISA to Relational Model}
  
  \begin{goal}{Method 2: many tables}
    Form a table for each entity set with all local and inherited attributes.
  \end{goal}
  
  \emph{If specialisation is total} then we need no table for the generalised entity (\textit{person}):
  \pause
  \begin{exampleblock}{}
    Table for the \emph{generalised entity set} 
    can be defined \emph{as a view} containing the union of the specialisation tables
  \end{exampleblock}
  \pause
  \begin{alertblock}{}
    \emph{Drawback:} 
    \begin{itemize}
      \item 
        explicit table for the generalised entity might be needed for foreign key constraints.
      \item 
        attributes are stored redundantly if an entity belongs
        to several specialised entity sets (overlapping ISA)
        \begin{itemize}
          \item e.g. name and address are stored multiple times 
            for someone who is customer and employee
        \end{itemize}
    \end{itemize}
  \end{alertblock}      
\end{frame}