Paper: Mildly Non-Projective Dependency Structures

ACL ID P06-2066
Title Mildly Non-Projective Dependency Structures
Venue Annual Meeting of the Association of Computational Linguistics
Session Poster Session
Year 2006

Syntactic parsing requires a fine balance between expressivity and complexity, so that naturally occurring structures can be accurately parsed without compromising efficiency. In dependency-based parsing, several constraints have been proposed that restrict the class of permissible structures, such as projectivity, planarity, multi-pla- narity, well-nestedness, gap degree, and edge degree. While projectivity is gener- ally taken to be too restrictive for natural language syntax, it is not clear which of the other proposals strikes the best balance be- tween expressivity and complexity. In this paper, we review and compare the different constraints theoretically, and provide an ex- perimental evaluation using data from two treebanks, investigating how large a propor- tion of the structures ...