Ludovic Mignot

Partial derivatives of an extended regular expression

The notion of expression derivative due to Brzozowski leads to the construction of a deterministic automaton from an extended regular expression, whereas the notion of partial derivative due to Antimirov leads to the construction of a non-deterministic automaton from a simple regular expression. In this paper, we generalize Antimirov partial derivatives to regular expressions extended to complementation and intersection. For a simple regular expression with n symbols, Antimirov automaton has at most n+1 states. As far as an extended regular expression is concerned, we show that the number of states can be exponential.

Acyclic automata and small expressions using multi-tilde-bar operators

A regular expression with n occurrences of symbol can be converted into an equivalent automaton with (n+1) states, the so-called Glushkov automaton of the expression. Conversely, it is possible to decide whether a given (n+1)-state automaton is a Glushkov one and, if so, to convert it back to an equivalent regular expression of width n. Our goal is to extend the class of automata for which such a linear retranslation is possible. We define new regular operators, called multi-tilde-bars, allowing us to simultaneously apply a multi-tilde operator and a multi-bar one to a list of expressions. The main results are that a multi-tilde-bar expression of width n can be converted into an (n+1)-state position-like automaton and that any acyclic n-state automaton can be turned into an extended expression of width O(n).

A general framework for the derivation of regular expressions

The aim of this paper is to design a theoretical framework that allows us to perform the computation of regular expression derivatives through a space of generic structures. Thanks to this formalism, the main properties of regular expression derivation, such as the finiteness of the set of derivatives, need only be stated and proved one time, at the top level. Moreover, it is shown how to construct an alternating automaton associated with the derivation of a regular expression in this general framework. Finally, Brzozowski’s derivation and Antimirov’s derivation turn out to be a particular case of this general scheme and it is shown how to construct a DFA, a NFA and an AFA for both of these derivations.

Approximate regular expressions and their derivatives

Several studies have been achieved to construct a finite automaton that recognizes the set of words that are at a bounded distance from some word of a given language. In this paper, we introduce a new family of regular operators based on a generalization of the notion of distance and we define a new family of expressions, the approximate regular expressions. We compute Brzozowski derivatives and Antimirov derivatives of such operators, which allows us to provide two recognizers for the language denoted by any approximate regular expression.

Generalized one-unambiguity

Bruggemann-Klein and Wood have introduced a new family of regular languages, the one-unambiguous regular languages, a very important notion in XML DTDs. A regular language L is one-unambiguous if and only if there exists a regular expression E over the operators of sum, catenation and Kleene star such that L(E) = L and the position automaton of E is deterministic. It implies that for a one-unambiguous expression, there exists an equivalent linear-size deterministic recognizer. In this paper, we extend the notion of one-unambiguity to weak one-unambiguity over regular expressions using the complement operator ¬. We show that a DFA with at most (n + 2) states can be computed from a weakly one-unambiguous expression and that it is decidable whether or not a given DFA recognizes a weakly one-unambiguous language.

Two-Sided Derivatives for Regular Expressions and for Hairpin Expressions

The aim of this paper is to design the polynomial construction of a finite recognizer for hairpin completions of regular languages. This is achieved by considering completions as new expression operators and by applying derivation techniques to the associated extended expressions called hairpin expressions. More precisely, we extend partial derivation of regular expressions to two-sided partial derivation of hairpin expressions and we show how to deduce a recognizer for a hairpin expression from its two-sided derived term automaton, providing an alternative proof of the fact that hairpin completions of regular languages are linear context-free.

Multi-tilde-bar derivatives

Multi-tilde-bar operators allow us to extend regular expressions. The associated extended expressions are compatible with the structure of Glushkov automata and they provide a more succinct representation than standard expressions. The aim of this paper is to examine the derivation of multi-tilde-bar expressions. Two types of computation are investigated: Brzozowski derivation and Antimirov derivation, as well as the construction of the associated automata.

Multi-tilde Operators and Their Glushkov Automata

Classical algorithms convert arbitrary automata into regular expressions that have an exponential size in the size of the automaton. There exists a well-known family of automata, obtained by the Glushkov construction (of an automaton from an expression) and named Glushkov automata, for which the conversion is linear. Our aim is to extend the family of Glushkov automata. A first step for such an extension is to define a new family of regular operators and to check that the associated extended expressions have good properties: existence of normal forms, succinctness with respect to equivalent simple expressions, and compatibility with Glushkov functions. This paper addresses this first step and investigates the case of multi-tilde operators.

A New Family of Regular Operators Fitting with the Position Automaton Computation

The aim of this paper is to define a new family of regular operators fitting with the construction of the position automaton. These new operators support the computation of the four Glushkov functions (Null, First, Last and Follow), which allows the conversion of an extended expression with n symbol occurrences into a position automaton with n + 1 states.

k,l-Unambiguity and Quasi-Deterministic Structures: An Alternative for the Determinization

We focus on the family of k,l-unambiguous automata that encompasses the one of deterministic k-lookahead automata introduced by Han and Wood. We show that this family presents nice theoretical properties that allow us to compute quasi-deterministic structures. These structures are smaller than DFAs and can be used to solve the membership problem faster than NFAs.