21. A prosody structure generation apparatus comprising: a dialog information database which manages an entire dialog between a user and a system, and stores information and a dialog history required for the dialog to proceed based on a speech acts and intention; a system speaking style determination unit which determines a speech act and intention by analyzing a user utterance obtained through a speech recognition process with reference to the dialog information database, and determines the system speaking style as either read speech or dialog speech according to the determined speech act and intention associated with the user utterance; and a dialog prosody generation unit including a discourse information generation unit, a prosody information generation unit, and an intonation pattern generation unit, wherein the discourse information generation unit receives a user utterance from the system speaking style determination unit and generates a discourse information structure in which a different emphasis part is set according to whether the speech act and included semantic unit of a system utterance corresponding to whether the user utterance is new information or old information, wherein the prosody information generation unit receives discourse information structure from the discourse information generation unit, and a semantic structure, a sentence structure, and a morpheme structure of a system utterance, and generates prosody information in which an emphasis tag including an utterance boundary level, accent, and utterance duration is set on the basis of the types of semantic words, a closeness between polymorphemes, and a number of syllables that can be spoken at a time, wherein the utterance boundary level is adjusted based on closeness between semantic units, which is determined by syntax and case, and wherein the intonation pattern generation unit receives inputs of the semantic structure of a system utterance including prosody information, extracts a plurality of characteristics in each semantic unit and compares the plurality of characteristics with the characteristics of each semantic unit of an intonation pattern database with contents of characteristics of each semantic unit and their index, searches for a semantic unit having closest characteristics, and generates an intonation pattern according to a result of the search 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.
21. A prosody structure generation apparatus comprising: a dialog information database which manages an entire dialog between a user and a system, and stores information and a dialog history required for the dialog to proceed based on a speech acts and intention; a system speaking style determination unit which determines a speech act and intention by analyzing a user utterance obtained through a speech recognition process with reference to the dialog information database, and determines the system speaking style as either read speech or dialog speech according to the determined speech act and intention associated with the user utterance; and a dialog prosody generation unit including a discourse information generation unit, a prosody information generation unit, and an intonation pattern generation unit, wherein the discourse information generation unit receives a user utterance from the system speaking style determination unit and generates a discourse information structure in which a different emphasis part is set according to whether the speech act and included semantic unit of a system utterance corresponding to whether the user utterance is new information or old information, wherein the prosody information generation unit receives discourse information structure from the discourse information generation unit, and a semantic structure, a sentence structure, and a morpheme structure of a system utterance, and generates prosody information in which an emphasis tag including an utterance boundary level, accent, and utterance duration is set on the basis of the types of semantic words, a closeness between polymorphemes, and a number of syllables that can be spoken at a time, wherein the utterance boundary level is adjusted based on closeness between semantic units, which is determined by syntax and case, and wherein the intonation pattern generation unit receives inputs of the semantic structure of a system utterance including prosody information, extracts a plurality of characteristics in each semantic unit and compares the plurality of characteristics with the characteristics of each semantic unit of an intonation pattern database with contents of characteristics of each semantic unit and their index, searches for a semantic unit having closest characteristics, and generates an intonation pattern according to a result of the search 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. 23. The apparatus of claim 21 , wherein the system speaking style determination unit sets a criterion to determine a system speaking style, by determining the criterion statistically or experimentally in advance, corresponding to speech act and intention.