Nested-word automata (NWAs) are a language formalism that helps bridge the gap between finite-state automata and pushdown automata. NWAs can express some context-free properties, such as parenthesis matching, yet retain all the desirable closure characteristics of finite-state automata.

This paper describes OpenNWA, a C++ library for working with NWAs. The library provides the expected automata-theoretic operations, such as intersection, determinization, and complementation. It is packaged with WALi—the Weighted Automaton Library—and interoperates closely with the weighted pushdown system portions of WALi.

(Click here to access the paper: PDF; (c) Springer-Verlag.)