$\left[\begin{array}{l}\mathrm{sem}:$ \left[\begin{array}{l}\mathrm{periode}:$ \left[\begin{array}{l}\mathrm{type}:\; d\\ \mathrm{debut}:$ \left[\begin{array}{l}\mathrm{annees}:$ \left[\begin{array}{l}\mathrm{type}:\; milieu\\ \mathrm{annee}:\; 1980\end{array}\right]$\end{array}\right]$\end{array}\right]$\end{array}\right]$\\ \mathrm{axis}:\; time\end{array}\right]$