-- Semantics of Complex Sentences in Japanese --
Hiroshi Nakagawa, Tatsunori Mori
Dept. of Electronics and Computer Engineering, Yokohama National University
156 Tokiwadai, Hodogaya, Yokohama 240, Japan
e-mail: nakagawa@naklab.dnj.ynu.ac.jp
Our aim is to formalize constraints that are needed to develop a parser based on unification grammar (called ``UG'' henceforth) so that our parser can treat variety of types of sentences in Japanese. One important and necessary function when a parser processes discourses in Japanese, is the so called zero anaphora resolution. All of syntactic, semantic, and pragmatic aspects are to be involved to resolve zero anaphora. This year we concentrate our effort to semantics of complex sentences. Roughly speaking, the important part of semantics of complex sentence is formalized as relations among semantic roles that appear in the main clause or the subordinate clause. At first glance, the constraints about these relations are not local in terms of main or subordinate clauses. In other words, semantic roles that appear in subordinate clause and semantic roles that appear in the main clause are directly constrained by the constraints of complex sentences. However, looking more carefully, we find that the constraints of subordinate clause and the constraints of main clause are represented as local constraints by introducing the new notion of \it causer. More precisely, causer is one of the semantic roles that appear in a subordinate clause, and the constraints in subordinate clause are stated as identity relations between causer and other semantic roles in subordinate clause. Therefore these constraints are local in subordinate clause. The constraints in main clause are stated as identity relations between causer which comes from subordinate clause, and other semantic roles in main clause. Therefore we don't have to care about other semantic roles in subordinate clause than causer. In this sense, the constraints in the main clause can be treated as almost local constraints of the main clause. The next question is how to represent the semantics of complex sentences in feature structure. For this, we should write down the constraints about these relations among semantic and discourse roles in a feature structure formalism. Of course some of these constraints are about syntactic feature structures. However we here mainly pursue the constraints about semantic feature structures. In addition some of the constraints we deal with here may be reflected from pragmatic constraints.
Keywords: evidential modality, point of view, dialogue, Japanese discourse, discourse role, semantic role, feature structure