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Various parsing techniques have been developed for lexicalized grammars such as Lexicalized Tree Adjoining Grammar (LTAG) (Schabes et al., 1988), and Head-Driven Phrase Structure Grammar (HPSG) (Pollard and Sag, 1994). Along with the independent development of parsing techniques for individual grammar formalisms, some of them have been adapted to other formalisms (Schabes et al., 1988; van Noord, 1994; Yoshida et al., 1999; Torisawa et al., 2000). However, these realizations sometimes exhibit quite different performance in each grammar formalism (Yoshida et al., 1999; Yoshinaga et al., 2001). . | Comparison between CFG filtering techniques for LTAG and HPSG Naoki Yoshinagaf f University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-0033 Japan yoshinag@is.s.u-tokyo.ac. Kentaro Torisawa Ị Japan Advanced Institute of Science and Technology 1-1 Asahidai Tatsunokuchi Ishikawa 923-1292 Japan torisawa@jaist.ac.jp Jun ichi Tsujiif CREST JST Japan Science and Technology Corporation Hon-cho 4-1-8 Kawaguchi-shi Saitama 332-0012 Japan tsujii@is.s.u-tokyo.ac.jp Abstract An empirical comparison of CFG filtering techniques for LTAG and HPSG is presented. We demonstrate that an approximation of HPSG produces a more effective CFG filter than that of LTAG. We also investigate the reason for that difference. 1 Introduction Various parsing techniques have been developed for lexicalized grammars such as Lexicalized Tree Adjoining Grammar LTAG Schabes et al. 1988 and Head-Driven Phrase Structure Grammar HPSG Pollard and Sag 1994 . Along with the independent development of parsing techniques for individual grammar formalisms some of them have been adapted to other formalisms Schabes et al. 1988 van Noord 1994 Yoshida et al. 1999 Torisawa et al. 2000 . However these realizations sometimes exhibit quite different performance in each grammar formalism Yoshida et al. 1999 Yoshinaga et al. 2001 . If we could identify an algorithmic difference that causes performance difference it would reveal advantages and disadvantages of the different realizations. This should also allow us to integrate the advantages of the realizations into one generic parsing technique which yields the further advancement of the whole parsing community. In this paper we compare CFG filtering techniques for LTAG Harbusch 1990 Poller and Becker 1998 and HPSG Torisawa et al. 2000 Kiefer and Krieger 2000 following an approach to parsing comparison among different grammar formalisms Yoshinaga et al. 2001 . The key idea of the approach is to use strongly equivalent grammars which generate equivalent parse results for the .
