Schéma tikz

\begin{tikzpicture}
  \draw[thick] (0,0) rectangle (4,2);
  \draw[thick] (8,0) rectangle (12,2);
  \draw[thick] (4,-4) rectangle (8,-2);
  \draw[thick,>=latex,->] (4,1.25)--(8,1.25);
  \draw[thick,>=latex,<-] (4,.75)--(8,.75);
  \draw[thick,>=latex,->] (2,0)--(4.5,-2);
  \draw[thick,>=latex,<-] (2.5,0)--(5,-2);
  \draw[thick,>=latex,->] (10,0)--(7.5,-2);
  \draw[thick,>=latex,<-] (9.5,0)--(7,-2);
\end{tikzpicture}

\begin{tikzpicture}
  \node[draw] (A) at (2,1) {\begin{minipage}{4cm}Un texte intéressant qui parle de trucs et d'autres\end{minipage}};
  \node[draw] (B) at (10,1) {\begin{minipage}{4cm}Un autre texte encore plus intéressant qui parle de trucs et d'autres\end{minipage}};
  \node[draw] (C) at (6,-2) {\begin{minipage}{4cm}Un autre texte encore plus intéressant qui parle de trucs et d'autres\end{minipage}};
  \draw[thick,>=latex,->] (A.-30)--(C.150);
  \draw[thick,>=latex,<-] (A.-18)--(C.125);
  \draw[thick,>=latex,->] (B.-145)--(C.30);
  \draw[thick,>=latex,<-] (B.-158)--(C.55);
  \draw[thick,>=latex,->] (A.5)--(B.175);
  \draw[thick,>=latex,<-] (A.-5)--(B.185);
  \draw[thick,>=latex,<-] (B.-158)--(C.55);
\end{tikzpicture}