\begin{frame}
  \frametitle{ANSI SPARC Architecture: 3 levels}

  \begin{block}{}
    \begin{center}
      \begin{tikzpicture}[default,node distance=13mm,nodes={rectangle,draw,thick,inner sep=2mm,fill=blue!80!green!20}]
        \node (p) {physical level};
        \node (l) [above of=p] {logical level};
        \node (v2) [above of=l,xshift=-10mm,node distance=15mm] {view 2};
        \begin{scope}[node distance=18mm]
        \node (v1) [left of=v2,node distance=23mm] {view 1};
        \node (v3) [right of=v2,draw=none,fill=none] {\ldots};
        \node (vn) [right of=v3] {view n};
        \end{scope}
        \node (u1) [draw=none,fill=none,above of=v1,node distance=11mm] {\includegraphics[height=1.3cm]{images/user_blue.png}};
        \node (un) [draw=none,fill=none,above of=vn,node distance=11mm] {\includegraphics[height=1.3cm]{images/user_green.png}};
        \begin{pgfonlayer}{background}
          \draw [fill=blue!5] ($(v1.north west)+(-3mm,16mm)$) rectangle ($(vn.south east)+(3mm,-3mm)$);
          \coordinate (view) at ($(v1.south west)!.5!(vn.south east)+(3mm,-3mm)$);
        \end{pgfonlayer}
        \begin{scope}[nodes={draw=none,fill=none}]
        \node at (4cm,0) [anchor=west,align=left] {Physical\\(Internal)};
        \node at (4cm,15mm) [anchor=west,align=left] {Logical\\(Conceptual)};
        \node at (4cm,33mm) [anchor=west,align=left] {View\\(External)};
        \end{scope}
        \draw (p) -- (l) |- (view);
      \end{tikzpicture}
    \end{center}
  \end{block}

  \begin{itemize}
    \item Different applications might use different views
    \item Data stored once at physical level (good for consistency)
  \end{itemize}
\end{frame}