\begin{frame} \frametitle{Null Values} The relational model allows \textbf{missing attribute values}.\\ (Table entries may be empty.) \bigskip \begin{center}\vspace{-2ex} \scalebox{1}{{\ttfamily\tableStudents}} \vspace{-1ex} \end{center} \medskip \begin{goal}{} Formally, the set of possible values (the domain) for an attribute is extended by a new special value \emph{``null''}. \end{goal} \pause \begin{alertblock}{} This ``null'' is \emph{not} the number 0 or the empty string. \\A null value is different from all values of any data type. \hfill\smash\textdbend \end{alertblock} \end{frame}