OpenFst: A General and Efficient Weighted Finite-State Transducer Library

(Extended Abstract of an Invited Talk)
  • Cyril Allauzen
  • Michael Riley
  • Johan Schalkwyk
  • Wojciech Skut
  • Mehryar Mohri
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4783)


We describe OpenFst, an open-source library for weighted finite-state transducers (WFSTs). OpenFst consists of a C++ template library with efficient WFST representations and over twenty-five operations for constructing, combining, optimizing, and searching them. At the shell-command level, there are corresponding transducer file representations and programs that operate on them. OpenFst is designed to be both very efficient in time and space and to scale to very large problems.

This library has key applications speech, image, and natural language processing, pattern and string matching, and machine learning.

We give an overview of the library, examples of its use, details of its design that allow customizing the labels, states, and weights and the lazy evaluation of many of its operations.

Further information and a download of the OpenFst library can be obtained from


weighted automata finite-state transducers rational power series 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • Cyril Allauzen
    • 1
  • Michael Riley
    • 2
  • Johan Schalkwyk
    • 2
  • Wojciech Skut
    • 2
  • Mehryar Mohri
    • 1
  1. 1.Courant Institute of Mathematical Sciences, 251 Mercer ST, New York, NY 10012USA
  2. 2.Google, Inc., 111 Eighth AV, New York, NY 10011USA

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