Firstly, to restrict the training data to grammatical and informative sentences, only news articles satisfying certain conditions are used.
then, nouns, verbs, adjectives, and adverbs (i.e., content words) shared by S and H are identified by matching word lemmas, and a rooted dependency subtree that contains all the shared content words is regarded as C. their method is designed for English, and cannot be applied to Japanese as it is.