Automata Equipped with Auxiliary Data Structures and Regular Realizability Problems

TL;DR

This paper explores automata models with auxiliary data structures, connecting their non-emptiness problems to regular realizability problems and analyzing their computational complexity.

Contribution

It introduces a formal framework linking automata with auxiliary data structures to regular realizability problems, unifying various automata models and complexity results.

Findings

Non-emptiness problem for automata with ADS is equivalent to a regular realizability problem.

Languages recognized by nondeterministic log-space Turing machines with ADS are connected to the non-emptiness problem.

Complexity of these problems is the same up to log-space reductions.

Abstract

We consider general computational models: one-way and two-way finite automata, and logarithmic space Turing machines, all equipped with an auxiliary data structure (ADS). The definition of an ADS is based on the language of protocols of work with the ADS. We describe the connection of automata-based models with ``Balloon automata'' that are another general formalization of automata equipped with an ADS presented by Hopcroft and Ullman in 1967. This definition establishes the connection between the non-emptiness problem for one-way automata with ADS, languages recognizable by nondeterministic log-space Turing machines equipped with the same ADS, and a regular realizability problem (NRR) for the language of ADS' protocols. The NRR problem is to verify whether the regular language on the input has a non-empty intersection with the language of protocols. The computational complexity of these problems (and languages) is the same up to log-space reductions.