OpenFst Extensions

The following extensions to OpenFst are available. These are built only if the configure flags are provided as below. Also provided are the include files and the libraries to be used in client code.

Compact FSTs

Compact FSTs use space-efficient representations of specialized FSTs such as acceptors, strings or unweighted FSTS. This extension has libraries that register CompactFst for uint8, uint16, and uint64 representable total arcs. CompactFst for uint32 is registered in libfst.{a,so}. See here for more details, including how to load dynamically.

Const FSTs

A ConstFst is a general-purpose immutable FST. This extension has libraries that register ConstFst for uint8, uint16, and uint64 representable total arcs. ConstFst for uint32 is registered in libfst.{a,so}. See here for more details, including how to load dynamically.

FST Archives (FARs)

A finite-state archive (FAR) is used to store an indexable collection of FSTs in a single file. Utilities are provided to create FARs from FSTs, to iterate over FARs, and to extract specific FSTs from FARs. See the source code for additional information.

Look-Ahead FSTs

A look-ahead FST is an immutable FST that has a lookahead matcher, selected for more efficient composition in a particular application. When used in composition, no special options need to be passed; the appropriate matcher and filter are selected automatically. This extension has libraries that register label and transition lookahead FSTs. See here for more details, including how to load dynamically.

Push-down Transducers (PDTs)

This is an experimental push-down transducer (PDT) library. A PDT is encoded as an FST, where some transitions are labeled with open or close parentheses. To be interpreted as a PDT, the parentheses must balance on a path. See the header files for additional information.