Diagnostic Processing of Japanese for Computer-Assisted Second Language Learning

Diagnostic Processing of Japanese for Computer-Assisted Second Language Learning Jun’ichi Kakegawa, Hisayuki Kanda, Eitaro Fujioka, Makoto Itami, Kohji Itoh Department of Applied Electronics, Science University of Tokyo 2641 Yamazaki, Noda-shi, Chiba-ken 278-8510, JAPAN {kakegawa,kanda,eitaro76,itami,itoh}@itlb.te.noda.sut.ac.jp Abstract As an application of NLP to computer-assisted language learn- ing(CALL) , we propose a diag- nostic processing of Japanese be- ing able to detect errors and inap- propriateness of sentences composed by the students in the given situ- ation and the context of the exer- cise texts. Using LTAG(Lexicalized Tree Adjoining Grammar) formal- ism, we have implemented a proto- type of such a diagnostic parser as a component of a CALL system being developed. 1 Introduction In the recent classroom of second language learning, communicative approach(H.G. Wid- dowson, 1977) is promoted in which it mat- ters for the students to become aware of the language use, i.e. the functionality of lan- guage usage and it’s dependence on the sit- uations and the contexts of communication. In order to achieve the objective according to “constructivistic” point of view of learning (T.M.Duffy et al., 1991), the students are en- couraged to produce sentences by themselves in various situations and contexts and guided to recognize by themselves the erroneous or inappropriate functions of their misused ex- pressions. We have already proposed a Computer- Assisted Language Learning(CALL) system (N.Kato et al., 1997) which provides the stu- dents with sample texts promoting their re- flection on the errors and inappropriateness, detected by a diagnostic parser, of the sen- tences composed by the students filling the blanks set up in the given contexts and situ- ations. In this paper we report on prototyp- ing the diagnostic parser implemented using LTAG formalism as a component of the sys- tem. LTAG(Lexicalized Tree Adjoining Gram- mar) is a lexicalized grammatical formalism (XTAG Research Group, 1995). For ease of diagnosing the erroneous sentences com- posed by the students, lexicalized type of grammars seemed most suitable. Comparing HPSG(Head-driven Phrase Structure Gram- mar) (C.Pollard et al., 1994) and LTAG, the well-known two (almost-)lexicalized gram- mars, LTAG looked more simple and espe- cially convenient for sentence generation nec- essary in diagnosis. LTAG systematically as- sociates an elementary tree structure with a lexical anchor and the structure is embedded in the corresponding lexical item. Associated with each of the external nodes of the embed- ded tree structure are feature structures such as inflection, case information, head symbol, semantic constraints as well as a difference list for surface expressions. These features have their origin in the anchored lexical item. The feature information can, moreover, in- clude the knowledge of situated language use. Appearance of the features at the external nodes of the lexical items greatly facilitates generation of local phrases which is indispens- able in diagnostic parsing. These are the rea- son why we employed LTAG. Preference of unification to all-procedural handling excluded the so-called “ dependency grammar ”(M.Nagao, 1996). 2 LTAG of Japanese 2.1 The Characteristic of Japanese Japanese phrases are classified in the first place into two categories: …

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