\begin{frame}
  \frametitle{Foreign Keys and Notation}
  
  \begin{goal}{}
    \textbf{Only keys  may be referenced} (primary or secondary).\\
    \remark{References to non-key attributes are not permitted.}
  \end{goal}
  
  \begin{goal}{}
    A table with a composite key must be
    referenced with a \textbf{composite foreign key that has the same number of
    attributes and domains}.
  
    \remark{It is not required that the corresponding attributes have identical names.}
  \end{goal}
  \medskip
  
  Foreign keys are denoted with arrows ($\to$) in the schema.
  Composite keys appear in parentheses:
  
  \structureAll[0.85]
  
  \remark{Typically the primary key is referenced, so it suffices to list the target relation.}
\end{frame}