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\begin{frame}
\frametitle{Relationship Sets}

\movieexample
\bigskip
\begin{block}{}
A \emph{relationship \alert{set}} is set of relationships of the same kind.
\end{block}

That is, a \emph{relationship set} is a set of tuples $(e_1,e_2,\ldots,e_n)$
where $e_1 \in E_1$, \ldots, $e_n \in E_n$ are from entity sets $E_1,\ldots,E_n$.
\medskip

\alt<-1>{
\begin{exampleblock}{}
Example of a relationship set
{\small
\begin{talign}
\{ \; &(\text{Uma Thurman},\,\text{Pulp Fiction}),\;
(\text{Mark Hamill},\,\text{Star Wars}),\\
&(\text{Harrison Ford},\,\text{Star Wars}), \;
(\text{Harrison Ford},\,\text{Indiana Jones}) \;\}
\end{talign}}
The elements of a relationship set are relationships:
\begin{itemize}
\item $(\text{Mark Hamill},\,\text{Star Wars}) \in \text{shows}$\; is a relationship
\end{itemize}
\end{exampleblock}
}{
\begin{goal}{}
A relationship set \textit{plays-in} between
entity sets \textit{actor} and \textit{movie} is indicated as follows in E/R models:
\begin{center}
\scalebox{.85}{
\node[relationship] (plays) at ($(actor)!.5!(movie)$) {plays-in} edge (actor) edge (movie);