A Two-Level Dialogue Representation

A TWO-LEVEL D I ~ REPRESENTATION 1 Giacomo Ferrari Department of Linguistics University of Pisa Ronan Reilly Educational Research Centre St Patrick's College, Dublin 9 ABSTRACT In this paper a two level dialogue representation system is presented° It is intended to recognize the structure of a large range of dialogues including some nonverbal communicative acts which may be involved in an interaction. It provides a syntactic description of a dialogue which can be expressed in terms of re-writing rules. The semantic level of the proposed representation system is given by the goal and subgoal structure underlying the dialogue syntactic units. Two types of goal are identified; goals which relate to the content of the dialogue, and those which relate to cormaunicating the content° i. INTRODUCTION Research on computational modelling of discourse has highlighted some important aspects of hun~an dialogic communication. In some cases (Reichman, 1984), a structural description of linguistic communication has been attempted altklough not for proper dialogue. What is required is a structural description identifying a corresponding set of con~nunicative acts which can be confined in a fixed pattern, to form higher level communication act categories or dialogue constituents. The importance of such a structural description, if attained, is that it would make possible an axiomatic theory of dialogue, embedding rhetorical patterns, focusing, and focus shifting. A possible basis for such a structural description is Burton's (1981) taxonomy of communication acts, with some modifications. Such a formalization of dialogue, however, is a fully syntactic one which needs to be augmented with some semantics. Our assumption is that dialogue constituents have a semantic interpretation in terms of goals and subgoals. A theoretical frame for a dialogue classification system based on these assunptions is being developed with the aim of providing a coherent basis for the computational modelling of dialogue. The final aim of our project is, in fact the design and implementation of a computational dialogic interaction system, with the ability to recover fr~n communication failure. 2. STRUCZURAL DESCRIPTION The syntactic level of a dialogue description system has to meet three requirements: (a) It must consist of a model whose generality makes it applicable to both person-person and 1This research was supported in part by the ESPRIT progranme of the CEC under contract AIP P527. person-machine dialogues, irrespective of the socio-institutional disposition of any speaker/user. (b) It must be capable of describing in terms of communication concepts the i~teractive nature of dialogue exchanges. (c) It must be capable of "naming" the units which compose the dialogue exchanges, i.eo identifying an utterance as both of a particular type and playing a cez%ain role in a particular exchange. The dialogue units taxonomy proposed by Burton (].981) seems to satisfy these requirements. According to her analysis systen[ we distinguish four hierarchically related levels: the interaction~ which is the largest unit; the transaction; the exchange; the move; and the act. An interaction consists of a number of transactions, a transaction consists of a number of exchanges, and so on. ~e smallest interactive unit …

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