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Helsinki Finite-State Technology
Helsinki Finite-State Technology logo.png
Developer(s)HFST team
Initial release2008; 11 years ago (2008)
Stable release
3.11.0 / September 16, 2016; 2 years ago (2016-09-16)
Repository Edit this at Wikidata
Written inC++, Python, Java
Operating systemCross-platform: Linux, Mac OS X, Windows
Available inEnglish
TypeFinite-state toolkit
LicenseGPLv3, part Apache

Helsinki Finite-State Technology (HFST) is a computer programming library and set of utilities for natural language processing with finite-state automata and finite-state transducers. It is free and open-source software, released under a mix of the GNU General Public License version 3 (GPLv3) and the Apache License.


The library functions as an interchanging interface to multiple backends, such as OpenFST, foma and SFST. The utilities comprise various compilers, such as hfst-twolc (a compiler for morphological two-level rules),[1] hfst-lexc (a compiler for lexicon definitions) and hfst-regexp2fst (a regular expression compiler). Functions from Xerox's proprietary scripting language xfst is duplicated in hfst-xfst, and the pattern matching utility pmatch in hfst-pmatch, which goes beyond the finite-state formalism in having recursive transition networks (RTNs).

The library and utilities are written in C++, with an interface to the library in Python and a utility for looking up results from transducers ported to Java and Python.

Transducers in HFST may incorporate weights depending on the backend. For performing FST operations, this is currently only possible via the OpenFST backend. HFST provides two native backends, one designed for fast lookup (hfst-optimized-lookup), the other for format interchange. Both of them can be weighted.


HFST has been used for writing various linguistic tools, such as spell-checkers, hyphenators, and morphologies.[2][3] Morphological dictionaries written in other formalisms have also been converted to HFST's formats.[4]

See also[edit]


  1. ^ "A Short History of Two-Level Morphology".
  2. ^ "Open morphology for Finnish. Contribute to flammie/Omorfi development by creating an account on GitHub". 2019-02-23.
  3. ^ "How to Configure and Optimise Spellers".
  4. ^ "Helsinki Finite-State Technology - Browse /Resources at SourceForge.net".

External links[edit]


Lindén, Krister; Axelson, Erik; Drobac, Senka; Hardwick, Sam; Kuokkala, Juha; Niemi, Jyrki; Pirinen, Tommi; Silfverberg, Miikka (2013). "HFST - A System for Creating NLP Tools" (PDF). In Mahlow, Cersting; Piotrowski, Michael (eds.). Systems and Frameworks for Computational Morphology. Systems and Frameworks for Computational Morphology. Communications in Computer and Information Science. 380. Humboldt-Universität in Berlin: Springer. pp. 53–71.