Automatic Construction of Nominal Case Frames and its Application to Indirect Anaphora Resolution

Automatic Construction of Nominal Case Frames and its Application to Indirect Anaphora Resolution Ryohei Sasano, Daisuke Kawahara and Sadao Kurohashi Graduate School of Information Science and Technology, University of Tokyo {ryohei,kawahara,kuro}@kc.t.u-tokyo.ac.jp Abstract This paper proposes a method to auto- matically construct Japanese nominal case frames. The point of our method is the in- tegrated use of a dictionary and example phrases from large corpora. To examine the practical usefulness of the constructed nom- inal case frames, we also built a system of indirect anaphora resolution based on the case frames. The constructed case frames were evaluated by hand, and were confirmed to be good quality. Experimental results of indirect anaphora resolution also indicated the effectiveness of our approach. 1 Introduction What is represented in a text has originally a network structure, in which several concepts have tight relations with each other. However, because of the linear constraint of texts, most of them disappear in the normal form of texts. Automatic reproduction of such relations can be regarded as the first step of “text understand- ing”, and surely benefits NLP applications such as machine translation, automatic abstraction, and question answering. One of such latent relationship is indirect anaphora, functional anaphora, or bridging ref- erence, such as the following examples. (1) I bought a ticket. The price was 20 dollars. (2) There was a house. The roof was white. Here, “the price” means “the price of a ticket” and “the roof” means “the roof of a house.” Most nouns have their indispensable or req- uisite entities: “price” is a price of some goods or service, “roof” is a roof of some building, “coach” is a coach of some sport, and “virus” is a virus causing some disease. The relation between a noun and its indispensable entity is parallel to that between a verb and its argu- ments or obligatory cases. In this paper, we call indispensable entities of nouns obligatory cases. Indirect anaphora resolution needs a compre- hensive information or dictionary of obligatory cases of nouns. In case of verbs, syntactic structures such as subject/object/PP in English or case markers such as ga, wo, ni in Japanese can be utilized as a strong clue to distinguish several obliga- tory cases and adjuncts (and adverbs), which makes it feasible to construct case frames from large corpora automatically (Briscoe and Car- roll, 1997; Kawahara and Kurohashi, 2002). (Kawahara and Kurohashi, 2004) then utilized the automatically constructed case frames to Japanese zero pronoun resolution. On the other hand, in case of nouns, obliga- tory cases of noun Nh appear, in most cases, in the single form of noun phrase “Nh of Nm” in English, or “Nm no Nh” in Japanese. This sin- gle form can express several obligatory cases, and furthermore optional cases, for example, “rugby no coach” (obligatory case concerning what sport), “club no coach” (obligatory case concerning which institution), and “kyonen ‘last year’ no coach” (optional case). Therefore, the key issue to construct nominal case frames is to analyze “Nh of Nm” or …

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