Termination and Boundedness for Well-Structured Pushdown Systems

Well-structured pushdown systems (WSPDSs) extend pushdown systems with well-quasi-ordered (possibly in_nitely many) states and stack alphabet. As an expressive model for concurrent recursive computations, WSPDSs are believed to “be close the border of undecidability” [11]. Most of the decidability results are known only on subclasses. In this paper, we investigate the decidability of the termination and boundedness problems for WSPDSs using two algorithms: One is an extension of the reduced reachability tree technique proposed by Leroux et. al. in [11]. The other is based on Post^*-automata technique which has been successfully applied in the model checking of pushdown systems. The complexity of both are Hyper-Ackermannian for bounded WSPDSs. We implement both algorithms and make experiments on a large number of randomly generated WSPDSs. The results illustrate that the Post^*_automata based algorithm sometimes behaves an order of magnitude faster.
リサーチレポート（北陸先端科学技術大学院大学先端科学技術研究科情報科学系）