Most spoken dialogue systems that have been developed, such as airline information systems (Levin et al., 2000;Potamianos et al., 2000;San-Segundo et al., 2000) and train information systems (Allen et al., 1996;Sturm et al., 1999;Lamel et al., 1999), are categorized here.
it is not feasible to define such keywords in retrieval for operation manuals (Komatani et al., 2002) or WWW pages, where the target of retrieval is not organized and is written as natural language text.