Paper: Recovery of Empty Nodes in Parse Structures

ACL ID D07-1065
Title Recovery of Empty Nodes in Parse Structures
Venue Conference on Empirical Methods in Natural Language Processing
Session Main Conference
Year 2007

In this paper, we describe a new algorithm for recovering WH-trace empty nodes. Our approach combines a set of hand-written patterns together with a probabilistic model. Because the patterns heavily utilize regu- lar expressions, the pertinent tree structures are covered using a limited number of pat- terns. The probabilistic model is essen- tially a probabilistic context-free grammar (PCFG) approach with the patterns acting as the terminals in production rules. We eval- uate the algorithm’s performance on gold trees and parser output using three differ- ent metrics. Our method compares favorably with state-of-the-art algorithms that recover WH-traces.