Speech Dialogue Systems — A Pragmatics-Guided Approach to Rational Interaction

Modelling rational dialogues on the basis of FiniteState Automata has shown to be of limited use when natural speech behaviour and dynamic adaptation to new domains are an issue. To enable such a flexible, robust and generic dialog ue management, we rely on an approach characterized by a logica lly precise modelling of the linguistic and application aspect s of the domain in question and a dialogue manager deriving pragmati csdriven discourse strategies from reasoning on evolving bel i f structures, both of the user and the system. For the linguist ic part, we claim that a “pragmatics-first” view on rational interact ion provides an appropriate framework for flexible and scalable dialogue modelling. In particular, the plan-based approach offers the means to conduct taskor goal-oriented dialogues which aim at accomplishing concrete tasks. It enables cooperative re sponse behaviour and the ability for negotiation. For the reasoning part, i.e. knowledge representation and inference for the interp retation of dialogue as well as for planning to satisfy user goals in the application domain, we argue for a computational logic framework. By means of a clear functional separation betwee n the language model, the dialogue model, and the domain model , the feedback cycle between the dialogue manager and the applications is of vital importance, as is the close interac tion on the linguistic side occurring between the speech parser, the dialogue manager and the text generation module. I. GENERAL ASSUMPTIONS Our general goal is to build dialogue systems for rational interaction. What we want to achieve is the satisfaction of user goals in a given (ideally open) domain by conducting spoken dialogues where it should be possible in principle to augment them by other forms of multi-modal interaction like gestures or the selection of items from a menu on a screen. Interactions are called “rational” because we want to apply rationality principles (at the knowledge representation l eve ) to optimally select appropriate communicative actions. We assume that the satisfaction of user goals within the themat ic framework of a particular application domain is to be achiev ed with the help of a dialogue system proper in cooperation with a technical application which we also call the “domain proble m solver”. Such a technical application can be an information or reservation system, a system for controlling certain devic es, etc. In such settings, [1] characterize “practical systems” as taskor goal-oriented dialogue systems, where the dialogu e is focussed on accomplishing a concrete task. They claim tha t the conversational competence required for practical dial ogues is significantly simpler to achieve than general human conve rsational competence. We are convinced that this distinctio is useful because it provides a realistic starting point and be cause the latter – general human conversational competence – is hard to define. Hence, we begin with a certain well-defined conversational competence and with increasingly complex requirements from the application we can try to augment it, i.e., we attempt to proceed in an incremental fashion. But probably this will not be easy; we cannot expect that this can be done in the way of a linear progress: There may be fractions where completely different requirements come in which cann ot be integrated seamlessly. Another general underlying assumption is that for the interpretation of dialogue we insist on a clear commitment to a (computational) logic framework. Of course, humans act incoherently and even inconsistently, and common sense reasoning can only to a certain extent be understood in terms of logic, but we are convinced that a coherent and consistent rational reconstruction is the best we can do about it. Such a constructive perspective has the advantage of enabling us to begin with a well understood framework for knowledge representation and reasoning upon which we can attempt to build rule systems for still idealized, but more realisti c patterns of argumentation in specific domains. We believe th at there is a potential to succeed in a variety of prevailingly instrumentalized contexts as it is the case with technical pplications – that will be discussed in more detail below – r, to take up another example, in forensic argumentation. II. ON DIALOGUE MODELLING The question of scalability of natural language and speech dialogue systems has been an issue for quite a long time. And it becomes more and more pressing with the rapidly increasing processing power and memory size of modern hardware and the progress in software engineering techniqu es. Before we address the dimensions of scalability and the problems connected with it, let us have a look at history to sharpen our awareness. A. In the Beginning: The Structural Approach For several decades, natural language and speech systems for information dialogues have been developed on the basis of an approach which led from experimental systems to a commercially available technology. Although successful i n many domains, we will argue that those systems have severe limitations which are inherent to the underlying so-called structural approach.