1. A dialog prosody structure generating method comprising: generating discourse information based on a speech act of a user utterance for a semantic structure of a system utterance corresponding to the user utterance; generating prosody information including an utterance boundary level indicating a duration of a silent period between each semantic unit for the discourse information of the semantic structure, wherein the utterance boundary level is adjusted based on closeness between semantic units, which is determined by syntax and case; and generating an intonation pattern for the semantic structure of the system utterance based on the prosody information using by at least one computer system, wherein the speech act provides a speech act classification of the user utterance, so that even when speech acts are identical, the generated intonation pattern varies according to the speech act classification of the user utterance.