A Multilevel Approach To Handle Non-Standard Input

In the project "Procedural Dialogue Models" being carried on at the University of Bielefeld we have developed an Incremental multilevel parsing formalism to reconstruct task-oriented dialogues. A major difficulty we have had to overcome is that the dialogues are real ones with numerous ungrammatical utterances. The approach we have devised to cope with this problem is reported here. I THE INCREMENTAL, MULTILEVEL PARSING FORMALISM In recent NLU-systems a major importance is lald on processing non-standard input.l) The present paper reports on the experiences we have made in the project "Procedural Dialogue Models" reconstructing task~oriented dialogues, which were uttered in a rather colloquial German.2) To this aim we have developed an incremental multilevel parsing formalism (Christaller/Metzlng 82, Gehrke 82, Gehrke 83), based on an extension of the concept of cascaded ATNs (Woods 80). This formalism (see fig. A) organizes the interaction of several independent processing components, in our case 5. The processing components need not be ATNs; it is up to the user of the formalism to choose the tool for the specific task that suits her/hlm best. * The project is funded by the Deutsche Forschungsgemeinschaft. I) See e.g. session VIII in ACL 82, Carbonell 83, Kwasny 80, 'Sondheimer/Weischedel 80; for handling of ellipsis see Weischedel/ Sondheimer 82, Wahlster et al. 83. 2) The dialogues that we are working with were recorded in the City of Frankfurt/ Main (Klein 79). The first level, an ATN, is responsible for the syntactic analysis. Its main put ~ pose is to detect phrases as well as wh~ and imperative structures and to determine the syntactic status a phrase may have in the utterance. On this level the analysis of an utterance can reach a permissible final state even if there is no complete sentence structure derived. The decision, if permissible or not, is made on the pragmatic level. The semantic interpretation is carried out by a case-oriented production rule system. According to the incremental manner of processing there are two defini ~ tions of case slots: i. a general one for a tentative categorization of phrases before the main verb is detected, and 2. a specific one, connected with the respective verb frame. This double definition of case slots enables the parsing formalism to make a minimal interpretation of parts of the utterance in the case of a missing verb and thus gives suggestions for filling this gap. The QUESTION-ANSWER-INTERACTION~compo~ nent is an ATN. It has to categorize an utterance as a question, a part of an answer or as communication maintaining categories such as assurance, confirmation etc. This component is also responsible for recognizing a dialogue within in a dialogue when e.g. some clarification on that dialogue takes place. Finally the TASK-COMMUNICATION-component is itself a two-level cascade. One stage, the TASK-INTERACTION-component, provides the formalism with a dialogue scheme that presumably is applicable to most types of information-giving dialogues. The other stage, the TASK-SPECIFICATION-component, is responsible for the