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\begin{frame}
  \frametitle{Entity Sets}

  \begin{block}{}
    \begin{itemize}
      \item \emph{entity} is an abstract object
        \begin{itemize}
          \item e.g.: specific person, company, event
        \end{itemize}
    \pause
      \item entities have \emph{attributes}
        \begin{itemize}
          \item e.g.: people have names and addresses
        \end{itemize}
    \pause
      \item \emph{entity set} is a collection of similar entities 
        \begin{itemize}
          \item similar = sharing the same properties (attributes)
          \item e.g.: set of all persons, companies, trees, holidays
        \end{itemize}
    \end{itemize}
  \end{block}
  \bigskip
  \pause
  
  Comparison with object-oriented programming:
  \begin{itemize}
    \item entity $\approx$ object
    \item entity set $\approx$ class
  \end{itemize}
  \medskip
  \pause
  
  Important difference: the \emph{E/R model is static}
  \begin{itemize}
    \item models structure of the data, not the operations
    \item no methods/functions associated to entity sets
  \end{itemize}
\end{frame}