Deterministic automata for extended regular expressions

In this work we present the algorithms to produce deterministic finite automaton (DFA) for extended operators in regular expressions like intersection, subtraction and complement. The method like “overriding” of the source NFA(NFA not defined) with subset construction rules is used. The past work described only the algorithm for AND-operator (or intersection of regular languages); in this paper the construction for the MINUS-operator (and complement) is shown.

INSIDE THE CLASS OF REGEX LANGUAGES

We study different possibilities of combining the concept of homomorphic replacement with regular expressions in order to investigate the class of languages given by extended regular expressions with backreferences (REGEX). It is shown in which regard existing and natural ways to do this fail to reach the expressive power of REGEX. Furthermore, the complexity of the membership problem for REGEX with a bounded number of backreferences is considered.

COMPRESSED MEMBERSHIP PROBLEMS FOR REGULAR EXPRESSIONS AND HIERARCHICAL AUTOMATA

Membership problems for compressed strings in regular languages are investigated. Strings are represented by straight-line programs, i.e., context-free grammars that generate exactly one string. For the representation of regular languages, various formalisms with different degrees of succinctness (e.g., suitably extended regular expressions, hierarchical automata) are considered. Precise complexity bounds are derived. Among other results, it is shown that the compressed membership problem for regular expressions with intersection is PSPACE-complete. This solves an open problem of Plandowski and Rytter.

ANTIMIROV AND MOSSES'S REWRITE SYSTEM REVISITED

Antimirov and Mosses proposed a rewrite system for deciding the equivalence of two (extended) regular expressions. They argued that this method could lead to a better average-case algorithm than those based on the comparison of the equivalent minimal deterministic finite automata. In this paper we present a functional approach to that method, prove its correctness, and give some experimental comparative results. Besides an improved functional version of Antimirov and Mosses's algorithm, we present an alternative one using partial derivatives. Our preliminary results lead to the conclusion that, indeed, these methods are feasible and, most of the time, faster than the classical methods.