Small extended expressions for acyclic automata

Abstract

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 size 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 result is that any acyclic n-state automaton can be turned into an extended expression of size O(n). © 2009 Springer Berlin Heidelberg.