PROIEL treebank utility library


Gem Version


This is a utility library for reading and manipulating treebanks that use the PROIEL annotation scheme and the PROIEL XML-based interchange format.


This library requires Ruby >= 2.7 (as this is what Nokogiri 1.14.x requires).

Install as

gem install proiel

Getting started

The recommended way to use this library in your application is with bundler. Create a Gemfile with the following content:

source ''
gem 'proiel', '~> 1.0'

and then execute


To download a sample treebank, initialize a new git repository and add the PROIEL treebank as a submodule:

git init
mkdir vendor
git submodule add --depth 1 vendor/proiel-treebank

Here is a skeleton programme to get you started. Save this as myproject.rb:

#!/usr/bin/env ruby
require 'proiel'

tb =
Dir[File.join('vendor', 'proiel-treebank', '*.xml')].each do |filename|
  puts "Reading #{filename}..."

tb.sources.each do |source|
  source.divs.each do |div|
    div.sentences.each do |sentence|
      sentence.tokens.each do |token|
        # Do something

You can now run this as:

bundle exec ruby myproject.rb

See the wiki for more information.


proiel aims to adhere to Semantic Versioning 2.0.0. This means that a patch version or minor version should not break backward compatibility of a public API, and that breaking changes should only be introduced with new major versions. When specifying a dependency on this gem it is best practice to use a pessimistic version constraint with two digits of precision:

spec.add_dependency 'proiel', '~> 1.0'


Check out the git repository from GitHub and run bin/setup to install all development dependencies. Then run rake to run the tests.

You can also run bin/console for an interactive prompt to experiment with.

To install a development version of this gem, run bundle exec rake install.

To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the gem to


Documentation can be generated using YARD:



Bug reports and pull requests are welcome on GitHub at