\begin{frame} \frametitle{Eliminating Tables} If participation is \emph{partial} ($0\sldots 1$) then replacing the table by an attribute will result in \emph{null values} for the entities that do not participate in the relationship set. \begin{goal}{} If participation is \emph{total} ($1\sldots 1$), declare foreign key \sql{not null}. \end{goal} \pause \begin{goal}{} For \emph{one-to-one} ($0\sldots 1$ or $1\sldots 1$) relationship sets either side can be extended with the key of the other. \end{goal} \pause \begin{goal}{} Tables for relationship sets linking \emph{weak entity sets} to the identifying entity set can always be eliminated. \smallskip \emph{No extra table is needed!} The table of the weak entity set already contains the key of the identifying entity set. \end{goal} \remark{% For instance the \textit{payment} table already contains the full information that would appear in the \textit{loan-payment} table (\textit{loan-number} and \textit{payment-number}). } \end{frame}