\begin{figure}
  \centering
  \begin{tikzpicture}
    % Nodes
    \node[align=center]  (qap) [text width=1.5cm] at (0, 0)
    {QAP \scriptsize $\Ecal \cap \Ncal \cap \Ocal$};
    \node[align=center]  (gw) [text width=1cm] at (-2.5, 0)
    {GW  \scriptsize $\Ecal \cap \Ncal$};
    \node[align=center]  (ogw) [text width=1cm] at (2.5, 0)
    {$\ogw$ \scriptsize $\Ecal \cap \Ocal$};
    % Arrays
    \draw[->] (qap) -- (gw);
    \draw[->] (qap) -- (ogw);
  \end{tikzpicture}
  \caption{Connection between QAP and GW, $\ogw$}
  \label{fig:conn_qap_gw_ogw}
\end{figure}