A linear-time transition system for crossing interval trees

Abstract

We define a restricted class of non-projective trees that 1) covers many natural language sentences; and 2) can be parsed exactly with a generalization of the popular arc-eager system for projective trees (Nivre, 2003). Crucially, this generalization only adds constant overhead in run-time and space keeping the parser's total run-time linear in the worst case. In empirical experiments, our proposed transition-based parser is more accurate on average than both the arc-eager system or the swap-based system, an unconstrained nonprojective transition system with a worst-case quadratic runtime (Nivre, 2009).