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FoLiA-tools contains various Python-based command line tools for working with FoLiA XML (Format for Linguistic Annotation)

Project description

FoLiA: Format for Linguistic Annotation

by Maarten van Gompel, Radboud University Nijmegen

FoLiA is an XML-based annotation format, suitable for the representation of linguistically annotated language resources. FoLiA’s intended use is as a format for storing and/or exchanging language resources, including corpora. Our aim is to introduce a single rich format that can accommodate a wide variety of linguistic annotation types through a single generalised paradigm. We do not commit to any label set, language or linguistic theory. This is always left to the developer of the language resource, and provides maximum flexibility.

XML is an inherently hierarchic format. FoLiA does justice to this by maximally utilising a hierarchic, inline, setup. We inherit from the D-Coi format, which posits to be loosely based on a minimal subset of TEI. Because of the introduction of a new and much broader paradigm, FoLiA is not backwards-compatible with D-Coi, i.e. validators for D-Coi will not accept FoLiA XML. It is however easy to convert FoLiA to less complex or verbose formats such as the D-Coi format, or plain-text. Converters are provided.

The main characteristics of FoLiA are:

  • Generalised paradigm - We use a generalised paradigm, with as few ad-hoc provisions for annotation types as possible.
  • Expressivity - The format is highly expressive, annotations can be expressed in great detail and with flexibility to the user’s needs, without forcing unwanted details. Moreover, FoLiA has generalised support for representing annotation alternatives, and annotation metadata such as information on annotator, time of annotation, and annotation confidence.
  • Extensible - Due to the generalised paradigm and the fact that the format does not commit to any label set, FoLiA is fairly easily extensible.
  • Formalised - The format is formalised, and can be validated on both a shallow and a deep level (the latter including tagset validation), and easily machine parsable, for which tools are provided.
  • Practical - FoLiA has been developed in a bottom-up fashion right alongside applications, libraries, and other toolkits and converters. Whilst the format is rich, we try to maintain it as simple and straightforward as possible, minimising the learning curve and making it easy to adopt FoLiA in practical applications.

The FoLiA format makes mixed-use of inline and stand-off annotation. Inline annotation is used for annotations pertaining to single tokens, whilst stand-off annotation in a separate annotation layers is adopted for annotation types that span over multiple tokens. This provides FoLiA with the necessary flexibility and extensibility to deal with various kinds of annotations.

Notable features are:

  • XML-based, UTF-8 encoded
  • Language and tagset independent
  • Can encode both tokenised as well as untokenised text + partial reconstructability of untokenised form even after tokenisation.
  • Generalised paradigm, extensible and flexible
  • Provenance support for all linguistic annotations: annotator, type (automatic or manual), time.
  • Used by various software projects and corpora, especially in the Dutch-Flemish NLP community



  • Maarten van Gompel & Martin Reynaert (2014). FoLiA: A practical XML format for linguistic annotation - a descriptive and comparative study; Computational Linguistics in the Netherlands Journal; 3:63-81; 2013.
  • Maarten van Gompel (2014). FoLiA: Format for Linguistic Annotation. Documentation. Language and Speech Technology Technical Report Series LST-14-01. Radboud University Nijmegen.

FoLiA Tools

A number of command-line tools are readily available for working with FoLiA, to various ends. The following tools are currently available:

  • foliavalidator – Tests if documents are valid FoLiA XML. Always use this to test your documents if you produce your own FoLiA documents!
  • foliaquery – Advanced query tool that searches FoLiA documents for a specified pattern, or modifies a document according to the query. Supports FQL (FoLiA Query Language) and CQL (Corpus Query Language).
  • foliaeval – Evaluation tool, can compute various evaluation metrics for selected annotation types, either against a gold standard reference or as a measure of inter-annotated agreement.
  • folia2txt – Convert FoLiA XML to plain text (pure text, without any annotations)
  • folia2annotatedtxt – Like above, but produces output simple token annotations inline, by appending them directly to the word using a specific delimiter.
  • folia2columns – This conversion tool reads a FoLiA XML document and produces a simple columned output format (including CSV) in which each token appears on one line. Note that only simple token annotations are supported and a lot of FoLiA data can not be intuitively expressed in a simple columned format!
  • folia2html – Converts a FoLiA document to a semi-interactive HTML document, with limited support for certain token annotations.
  • folia2dcoi – Convert FoLiA XML to D-Coi XML (only for annotations supported by D-Coi)
  • foliatree – Outputs the hierarchy of a FoLiA document.
  • foliacat – Concatenate multiple FoLiA documents.
  • foliacount – This script reads a FoLiA XML document and counts certain structure elements.
  • foliacorrect – A tool to deal with corrections in FoLiA, can automatically accept suggestions or strip all corrections so parsers that don’t know how to handle corrections can process it.
  • foliaid – Assigns IDs to elements in FoLiA documents
  • foliafreqlist – Output a frequency list on tokenised FoLiA documents.
  • foliamerge – Merges annotations from two or more FoLiA documents.
  • foliatextcontent – A tool for adding or stripping text redundancy, supports adding offset information.
  • alpino2folia – Convert Alpino-DS XML to FoLiA XML
  • dcoi2folia – Convert D-Coi XML to FoLiA XML
  • rst2folia – Convert ReStructuredText, a lightweight non-intrusive text markup language, to FoLiA, using docutils.

All of these tools are written in Python, and thus require a Python (2.7, 3 or higher) installation to run. More tools are added as time progresses.


The FoLiA tools are published to the Python Package Index and can be installed effortlessly using texttt{pip}, from the command-line, type:

$ pip install folia-tools

Add sudo to install it globally on your system, if you install locally, we strongly recommend you use virtualenv to make a self-contained Python environment.

If pip is not yet available, install it as follows:

On Debian/Ubuntu-based systems:

$ sudo apt-get install python-pip

On RedHat-based systems:

$ yum install python-pip

On Arch Linux systems:

$ pacman -Syu python-pip

On Mac OS X and Windows we recommend you install Anaconda or another Python distribution.

Alternatively, you can use easy_install. The FoLiA tools can also be obtained from github, and once downloaded and extracted, can be installed using python install.


To obtain help regarding the usage of any of the available FoLiA tools, please pass the -h option on the command line to the tool you intend to use. This will provide a summary on available options and usage examples. Most of the tools can run on both a single FoLiA document, as well as a whole directory of documents, allowing also for recursion. The tools generally take one or more file names or directory names as parameters.


Please consult the FoLiA website at for more!

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