template<typename date_type> 
class dst_day_calc_rule {
public:
  // types
  typedef date_type::year_type year_type;

  // construct/copy/destruct
  ~dst_day_calc_rule();

  // public member functions
  virtual date_type start_day(year_type) const;
  virtual std::string start_rule_as_string() const;
  virtual date_type end_day(year_type) const;
  virtual std::string end_rule_as_string() const;
};