class RubyXL::ChartFile

def attach_relationship(rid, rf)
  case rf
  when RubyXL::ChartColorsFile     then store_relationship(rf) # TODO
  when RubyXL::ChartStyleFile      then store_relationship(rf) # TODO
  when RubyXL::ChartUserShapesFile then store_relationship(rf) # TODO
  else store_relationship(rf, :unknown)
  end
end