\begin{frame}
  \frametitle{Entity Sets}

  \begin{block}{}
    An \emph{entity} is an abstract object
        \begin{itemize}
          \item e.g.: specific person, company, event
        \end{itemize}
    \smallskip
    Entities have \emph{attributes}
        \begin{itemize}
          \item e.g.: people have names and addresses
        \end{itemize}
    \smallskip
    An \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{block}
  \medskip
  \pause
  
  \begin{goal}{}
    \emph{Comparison with object-oriented programming:}
    \begin{talign}
      \text{entity $\approx$ object} &&
      \text{entity set $\approx$ class}
    \end{talign}
    \pause    
    Important difference: the \emph{ER 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{goal}
\end{frame}