data file path in a gem

I am trying to access a data list from inside a gem code, how should I
set the file path ..

here is my gem file structure :

my_extension

      --- my_extension.gemspec
      --- Gemfile
      --- Gemfile.lock
      >> lib
          >> my_extension
                    --- code_a.rb
                    --- code_b.rb
                    --- code_c.rb
           --- my_extension.rb
           >> my_data
                    --- data.yml

from inside code_a.rb, I am trying to load an array from the
data.yml : data = YAML::load(File.open("data.yml"))
how should I set the path ??

thanks for feedback