\documentclass[crop,tikz]{standalone}
\input{common-headers}
\input{sigles}

\begin{document}

\begin{tikzpicture}[scale=2,
  model/.style={draw},
  system/.style={draw,circle},
  arrowed/.style={auto,-Stealth,shorten <=2pt,shorten >=2pt,bend angle=10},
  darowed/.style={auto,double,Stealth-Stealth,shorten <=2pt,shorten >=2pt},
  validate/.style={arrowed},
  validate2/.style={arrowed,dashed},
  annotation/.style={font=\scriptsize}]
  
  \node[model] (M1) at ( 0, 0.7) {$\modelM$};
  \node[model] (W)  at ( 0, 0) {$\model{M}{S}$};
  
  \draw[validate] (M1) to node[annotation,swap] {validation $\sigma_{\modelM}$} (W);
  %\draw[validate,bend right] (M1) to node[annotation,swap] {validation} (W);
  
  % Returning diagram
  %\draw[validate2,bend right] (W) to (M1);

  % Separation
  \draw[dashed] (-1,-1) to [bend left=70] ( 1,-1);
  
  \node[system] (S) at ( 0,-0.8) {$S$};
  \draw[darowed] (W) to node[annotation,yshift=2pt] {expériences/mesures} (S);
\end{tikzpicture}

\begin{tikzpicture}[scale=2,
  model/.style={draw},
  system/.style={draw,circle},
  arrowed/.style={auto,-Stealth,shorten <=2pt,shorten >=2pt,bend angle=10},
  darowed/.style={auto,double,Stealth-Stealth,shorten <=2pt,shorten >=2pt},
  validate/.style={arrowed},
  validate2/.style={arrowed,dashed},
  abstract/.style={arrowed,thick},
  abstract2/.style={arrowed,dashed,thick},
  annotation/.style={font=\scriptsize}]
  
  \node[model] (M1) at (-1, 1) {$E_{\model{M}{1}}$};
  %\node[model] (M2) at ( 0, 1) {$M_2$};
  \node[model] (M3) at ( 1, 1) {$E_{\model{M}{2}}$};
  \node[model] (W)  at ( 0, 0) {$E_{\model{M}{S}}$};
  
  \draw[validate,bend left] (W.west) to node[annotation,swap] {$\sigma_{\model{M}{1}}$} (M1.south);
  %\draw[validate] (M2) to node[annotation] {validation} (W.north);
  \draw[validate,bend right] (W.east) to node[annotation] {$\sigma_{\model{M}{2}}$} (M3.south);
  
  \draw[abstract,bend left] (M1) to node[annotation,swap] {$a$} (M3);
  %\draw[abstract,bend left] (M2) to node[annotation] {abstraction} (M3);

  % Returning diagram
  %\draw[abstract2,bend left] (M2) to (M1);
  %\draw[abstract2,bend left] (M3) to (M2);
  %\draw[validate2,bend right] (W.north west) to (M1);
  %\draw[validate2,bend left] (W.north east) to (M2);
\end{tikzpicture}

\begin{tikzpicture}[scale=2]
  
\end{tikzpicture}

\end{document}