public int getMinJaar()
  {
    int jaar = 99999;

    // Itereer de datasets
    for (DataSet set: this.datasets)
    {
      for (Category cat: set.categories)
      {
        for (SubCategory scat: cat.subcategories)
        {
          SubCategory subcat = new SubCategory(scat.id, scat.naam, scat.datatype, scat.weight, scat.red, scat.green, scat.blue, false);

          for (Period per: scat.periods)
          {
            if (per.year < jaar)
            {
              jaar = per.year;
            }
          }
        }
      }
    }

    return jaar;
  }