Rails router automatically calculated for you the controller and named routes in the following scenarios:

  match "home/about"                 #=> maps to home#about with named route home_about_path
  match "about"                      #=> does not work because it cannot guess the controller
  match "about" => "home#about"      #=> maps to home#about with named route home_about_path
  match "home/about", :as => "about" #=> maps to home#about with named route about_path