ActiveRecord requires RAILS_ROOT for relative Sqlite path

I'm writing a little time tracking tool for Windows in Ruby. The data is stored in a database so I figured I'd use ActiveRecord and maybe learn something about Rails along the way. Everything I found about ActiveRecord tells me that it "can be used independently outside of Rails". One minor detail that I just figured out:

If you want to use a relative path for a sqlite3 database in your database.yml, you have to define RAILS_ROOT.

For example, if config/database.yml =>

production:
  adapter: sqlite3
  database: db/production.sqlite

ActiveRecord initialization (mine's in config/boot.rb) looks like:

RAILS_ROOT = "#{File.dirname(File.expand_path(__FILE__))}/.."
RAILS_ENV  = ENV['RAILS_ENV'] || 'production'

$LOAD_PATH.unshift "#{RAILS_ROOT}/vendor/sqlite3"
config = YAML::load(IO.read("#{RAILS_ROOT}/config/database.yml"))
ActiveRecord::Base.configurations = config
ActiveRecord::Base.establish_connection(config[RAILS_ENV])