Modality Expressions in Japanese and Their Automatic Paraphrasing

It is important for future NLP systems to formulate the semantic equivalence (and more generally, the semantic similarity) of natural language expressions. In particular, paraphrasing, full text information retrieval, example-based MT and document compression technology require the effective equivalence criterion for linguistic expressions. In this paper, first, we discuss the meaning of Japanese sentence-final modality expressions (ME) and second, present equivalence rules for paraphrasing a string of MEs while preserving its meaning.