template<typename date_type, typename time_duration_type, typename dst_traits> 
class dst_calc_engine {
public:
  // types
  typedef date_type::year_type                            year_type;    
  typedef date_type::calendar_type                        calendar_type;
  typedef dst_calculator< date_type, time_duration_type > dstcalc;      

  // public static functions
  time_is_dst_result 
  local_is_dst(const date_type &, const time_duration_type &) ;
  bool is_dst_boundary_day(date_type) ;
  time_duration_type dst_offset() ;
  date_type local_dst_start_day(year_type) ;
  date_type local_dst_end_day(year_type) ;
};