\begin{frame}
  \frametitle{Weak Entity Sets}

  \weakentityexample
  
  \begin{block}{}
    A \emph{weak entity set} is an entity set without a primary key.
    \pause
    \begin{itemize}
      \item The existence of a weak entity set depends on the existence of
            an \emph{identifying entity set}.
    \pause
      \item There must be a total, one-to-many relationship set
            from the identifying entity set to the weak entity set.
            This \emph{identifying relationship} is depicted by a double diamond. 
    \pause
      \item The $\disc{\text{\emph{discriminator}}}$ is a partial key,
            it distinguishes the\\[-.6ex] weak entity only in combination with the identifying entity.
    \pause
      \item Primary key of the weak entity set is a combination of the discriminator
            and primary key of the identifying entity set.
    \end{itemize}
    
  \end{block}
  \vspace{10cm}
\end{frame}