Anssi's derivative of SFST

AFST is Anssi's code branch of the Stuttgart Finite-State Tool (SFST) and closely related to HFST, Helsinki Finite-State Transducer Interface, that is also developed in Helsinki.

Modifications Policy

The distributed development of AFST and HFST code branches is based on practices that aim to keep them in sync as far as possible.

• Renamed files - When approriate, branch-specific code is kept in a separate files that is included to the SFST code.
• Indicate stable code - Each new file contains contains a stable and unstable block. This indicates to the other branches the stable code portions that could be adopted to them. The original SFST code is considered stable. The new code of AFST is currently all unstable.
• Deprecation - If stable code of any version is not easily fixable, it is commented out and replaced with a new code in a stand-off file.
• Maintain presentation - The presentation (spacing and order of definitions) is not changed if the algorithm is otherwise correct. Presentation of the stable code is improved only when SFST, HFST, and AFST developers agree on a cosmetic code upgrade.

Some Features of AFST

In AFST, there are some interesting addition to SFST. It is proposed that these will be reviewed, improved further and included to HFST and SFST.

• Utilities for prettyprinting finite-state networks according in various compatibility text formats that include: the matrix representation TWOLC and the list format used by XFST. Usable as commands "fst-tprint" and "fst-xprint". Needs further development.
• There is also a routine that produces a dot source for a nice visualization. This routine packs similar arcs and produces nice graphs. However, the current routine is based on slow extreme programming code that should be optimized and prettyprinted.
• There are routines that help testing the compiler: "test" and "draw". The first enables regression testing and parallel comparison with other finite-state tools. The second compiles file and produces xfig, ps, pdf, and epsi figures of transducers.
• There are a number of unstable algorithms that work in special situations, such as when the alphabet is closed. These include a better algorithm for asymmetric difference, a new algorithm for the shuffle and cross-product operations and some algorithms that manipulate auxiliary symbols.
• There are new unstable implementations of some basic operations. The new implementations support open alphabet (with the ANY symbol "<.>").
• The Makefile has been changed in such a way that the object code is stored to ../obj directory.

Downloads

The following versions of AFST are downloadable:

• SFST-1.1-20080208 - the closest ancestor of AFST-20080814.tgz
• AFST-20080814.tgz - the latest development version that is still unstable and under-documented.

Maintenance Plan

The maintenance of AFST is based on the following plans:

• AFST includes all the code of the latest SFST as long as possible. However, AFST has a lot of additions or improved algorithm implementations that have been merged with the SFST code when necessary, but larger additions are kept in separate files in order to keep the number of changes minimal.
• The development of AFST and HFST should merge. HFST is an interface between regular expression formalisms, such as the SFST programming language, and finite-state libraries such as the low-level implementation classes in SFST, OpenFST by Google Research and other similar packages such as Vaucanson. AFST contains, in addition to its extended SFST programming language and other formalisms, other extended parts of SFST, including extended implementation classes. Accordingly, there is a need to make HFST also AFST compliant. If HFST is going to include AFST extensions of SFST, we can say that HFST and AFST have merged.