Unlike the word-based operation, some of these models e.g (Knight and Marcu, 2000;Siddharthan et al., 2004;Turner and Charniak, 2005;Galanis and Androutsopoulos, 2010;Wang et al., 2013), are tree-based approaches that operate on the parse trees and thus the compression decision can be made for a constituent, instead of a single word.
if the hypothesis is incorrect, we update the feature weights using the structured perceptron learning strategy (Collins, 2002).