Railsのroutesでnamespaceとscopeの設定 ref: http://qiita.com/srockstyle/items/5b0bf6fe2a78e1aa7363

file0.txt

namespace :v3 do
    get "/test/read",:to=>"test#read"
end

file1.txt

GET  /v3/test/read(.:format)    v3/test#read

file2.txt

scope :v3 do
    get "/test/read",:to=>"test#read"
end

file3.txt

GET  /v3/test/read(.:format)    test#read

file4.txt

 12   namespace :artists do
 13     get 'similars/index'
 14     get 'similars/show'
 15     get 'tags/index'
 16     get 'tags/show'
 17   end

file5.txt

/artists/simmilar/index