Non-Projective Dependency Parsing in Expected Linear Time

We present a novel transition system for dependency parsing, which constructs arcs only between adjacent words but can parse arbitrary non-projective trees by swapping the order of words in the input. Adding the swapping operation changes the time complexity for deterministic parsing from linear to quadratic in the worst case, but empirical estimates based on treebank data show that the expected running time is in fact linear for the range of data attested in the corpora. Evaluation on data from five languages shows state-of-the-art accuracy, with especially good results for the labeled exact match score.

• Type: Journal
• Year: 2009
• Where: ACL
• Authors: Joakim Nivre
• Keywords: ACL 2009, Arbitrary Non-projective Trees, Computational Linguistics, Exact Match Score, Swapping Operation