      Tutorials (tutorial_id, tutorial, language_id, t_ord)
      Tutorials_Problems (tutorial_id, dataset_id, problem_id)
      Datasets (dataset_id, dataset)
      Dataset_Tables (dataset_id, ds_table, columns, dt_ord)
      Dataset_Sources (dataset_id, year, source)
      Problems (dataset_id, problem_id, points)
      Answers (dataset_id, problem_id, answer, priority)
      Questions (dataset_id, problem_id, q_ord, language_id, question)
      Problems_Categories (dataset_id, problem_id, category_id)
      Categories (category_id, category)
      Sessions (session_id, tutorial_id, login, password, points_min, points_max, ds_id, algorithm, help, host, start, stop, is_open)
      Sessions_Questions (session_id, dataset_id, problem_id, q_ord, language_id, answer, correct, time)
      Languages (language_id, language)
