Welcome to FAdo’s documentation

FAdo: Tools for Language Models Manipulation

Authors: Rogério Reis & Nelma Moreira

The support of transducers and all its operations, as well of Set Specifications, is a joint work with Stavros Konstantinidis (St. Mary’s University, Halifax, NS, Canada) (http://cs.smu.ca/~stavros/).

Contributions by

  • Marco Almeida

  • Ivone Amorim

  • Rafaela Bastos

  • Guilherme Duarte

  • Miguel Ferreira

  • Hugo Gouveia

  • Rizó Isrof

  • Eva Maia

  • Casey Meijer

  • Davide Nabais

  • João Pires

  • Meng Yang

  • Joshua Young

Page of the project: http://fado.dcc.fc.up.pt.

Version: 2.2.0

Copyright: 1999-2022 Rogério Reis & Nelma Moreira {rogerio.reis,nelma.moreira}@fc.up.pt

Faculdade de Ciências da Universidade do Porto

Centro de Matemática da Universidade do Porto

Licence:

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your Option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

What is FAdo?

The FAdo system aims to provide an open source extensible high-performance software library for the symbolic manipulation of automata and other models of computation.

To allow high-level programming with complex data structures, easy prototyping of algorithms, and portability (to use in computer grid systems for example), are its main features. Our main motivation is the theoretical and experimental research, but we have also in mind the construction of a pedagogical tool for teaching automata theory and formal languages.

Regular Languages

It currently includes most standard operations for the manipulation of regular languages. Regular languages can be represented by regular expressions (RegExp) or finite automata, among other formalisms. Finite automata may be deterministic (DFA), non-deterministic (NFA) or generalized (GFA). In FAdo these representations are implemented as Python classes.

Elementary regular languages operations as union, intersection, concatenation, complementation and reverse are implemented for each class. Also several other regular operations (e.g shuffle) and combined operations are available for specific models.

  • Several conversions between these representations are implemented:

    • NFA -> DFA: subset construction

    • NFA -> RE: recursive method

    • GFA -> RE: state elimination, with possible choice of state orderings (several heuristics)

    • RE -> NFA: Thompson, Glushkov/Position, epsilon-Follow, Follow, Partial Derivatives (naive and compressed RE), Prefix; and their duals.

    • SRE -> DFA: Brzozowski (SRE are RegExp ACIA, using sets)

    • RE -> DFA: AuPoint (Marked before) and YMG (Marked after)

  • For DFAs several minimization algorithms are available: Moore, Hopcroft, and some incremental algorithms. Brzozowski minimization is available for NFAs.

  • An algorithm for hyper-minimization of DFAs

  • For DFAs tests for reversability

  • Language equivalence of two DFAs can be determined by reducing their correspondent minimal DFA to a canonical form, or by the Hopcroft and Karp algorithm.

  • For NFAs reductions by left and right bisimilarity

  • Enumeration of the first words of a language or all words of a given length (Cross Section)

  • Some support for the transition semigroups of DFAs

Finite Languages

Special methods for finite languages are available:

  • Construction of a ADFA (acyclic finite automata) from a set of words

  • Minimization of ADFAs

  • Several methods for ADFAs random generation

  • Methods for deterministic cover finite automata (DCFA)

  • Special methods for Block languages where all words have the same length

Transducers

Several methods for transducers in standard form (SFT) are available:

  • Rational operations: union, inverse, reversal, composition, concatenation, Star

  • Test if a transducer is functional

  • Input intersection and Output intersection operations

Codes

A language property is a set of languages. Given a property specified by a transducer, several language tests are possible.

  • Satisfaction i.e. if a language satisfies the property

  • Maximality i.e. the language satisfies the property and is maximal

  • Properties implemented by transducers include: input preserving, input altering, trajectories, and fixed properties

  • Computation of the edit distance of a regular language, using input altering transducers

PRAX

Polynomial Random Approximation Algorithms allow to decide hard automata problems considering cetrain natural distributions on set of words.

In particular, using the notion of approximate universality

  • Test NFA universality for finite languagens

  • Test NFA universality for infinite languages using tractable word distributions (Lambert and Dirichlet)

Indices and tables