Departmental Papers (CIS)

Date of this Version

12-2006

Document Type

Conference Paper

Comments

From the 26th International Conference, Kolkata, India, December 13-15, 2006.

Abstract

We observe that pushdown tree automata (PTAs) known in the literature cannot express combinations of branching and pushdown properties. This is because a PTA processes the children of a tree node in possibly different control states but with identical stacks. We propose branching pushdown tree automata (BPTAs) as a solution. In a BPTA, a push-move views its matching pops as an unbounded, unordered set of successor moves and can assert existential and universal requirements on them, just the way finite automata on unranked, unordered trees pass requirements to the children of a tree node. We show that BPTAs can express some natural properties and are more expressive than PTAs. Using a small-model theorem, we prove their emptiness problem to be decidable. The problem becomes undecidable, however, if push-moves are allowed to specify the ordering of matching pops.

Subject Area

CPS Theory

Publication Source

Lecture Notes in Computer Science: FSTTCS 2006: Foundations of Software Technology and Theoretical Computer Science

Volume

4337

Start Page

393

Last Page

404

DOI

10.1007/11944836_36

Copyright/Permission Statement

The original publication is available at www.springerlink.com

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Date Posted: 26 June 2012