Power of Randomization in Automata on Infinite Strings

  • Authors:
  • Rohit Chadha;A. Prasad Sistla;Mahesh Viswanathan

  • Affiliations:
  • Univ. of Illinois, Urbana-Champaign and Univ. of Illinois, Chicago;Univ. of Illinois, Urbana-Champaign and Univ. of Illinois, Chicago;Univ. of Illinois, Urbana-Champaign and Univ. of Illinois, Chicago

  • Venue:
  • CONCUR 2009 Proceedings of the 20th International Conference on Concurrency Theory
  • Year:
  • 2009

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Abstract

Probabilistic Büchi Automata (PBA) are randomized, finite state automata that process input strings of infinite length. Based on the threshold chosen for the acceptance probability, different classes of languages can be defined. In this paper, we present a number of results that clarify the power of such machines and properties of the languages they define. The broad themes we focus on are as follows. We precisely characterize the complexity of the emptiness, universality, and language containment problems for such machines, answering canonical questions central to the use of these models in formal verification. Next, we characterize the languages recognized by PBAs topologically, demonstrating that though general PBAs can recognize languages that are not regular, topologically the languages are as simple as *** -regular languages. Finally, we introduce Hierarchical PBAs, which are syntactically restricted forms of PBAs that are tractable and capture exactly the class of *** -regular languages.