Talk’n’Travel: A Conversational System for Air Travel Planning

TALK'N'TRAVEL: A CONVERSATIONAL SYSTEM FOR AIR TRAVEL PLANNING David Stallard BBN Technologies, GTE 70 Fawcett St. Cambridge, MA, USA, 02238 Stallard@bbn.com Abstract We describe Talk'n'Travel, a spoken dialogue language system for making air travel plans over the telephone. Talk'n'Travel is a fully conversational, mixed-initiative system that allows the user to specify the constraints on his travel plan in arbitrary order, ask questions, etc., in general spoken English. The system operates according to a plan-based agenda mechanism, rather than a finite state network, and attempts to negotiate with the user when not all of his constraints can be met. Introduction This paper describes Talk'n'Travel, a spoken language dialogue system for making complex air travel plans over the telephone. Talk'n'Travel is a research prototype system sponsored under the DARPA Communicator program (MITRE, 1999). Some other systems in the program are Ward and Pellom (1999), Seneff and Polifroni (2000) and Rudnicky et al (1999). The common task of this program is a mixed-initiative dialogue over the telephone, in which the user plans a multi-city trip by air, including all flights, hotels, and rental cars, all in conversational English over the telephone. The Communicator common task presents special challenges. It is a complex task with many subtasks, including the booking of each flight, hotel, and car reservation. Because the number of legs of the trip may be arbitrary, the number of such subtasks is not known in advance. Furthermore, the user has complete freedom to say anything at any time. His utterances can affect just the current subtask, or multiple subtasks at once ("I want to go from Denver to Chicago and then to San Diego"). He can go back and change the specifications for completed subtasks. And there are important constraints, such as temporal relationships between flights, that must be maintained for the solution to the whole task to be coherent. In order to meet this challenge, we have sought to develop dialogue techniques for Talk'n'Travel that go beyond the rigid system- directed style of familiar IVR systems. Talk'n'Travel is instead a mixed initiative system that allows the user to specify constraints on his travel plan in arbitrary order. At any point in the dialogue, the user can supply information other than what the system is currently prompting for, change his mind about information he has previously given and even ask questions himself. The system also tries to be helpful, eliciting constraints from the user when necessary. Furthermore, if at any point the constraints the user has specified cannot all be met, the system steps in and offers a relaxation of them in an attempt to negotiate a partial solution with the user. The next section gives a brief overview of the system. Relevant components are discussed in subsequent sections. I System Overview The system consists of the following modules: speech recognizer, language understander, dialogue manager, state manager, language generator, and speech synthesizer. The modules 68 interact with each other via the central hub module of the Communicator Common Architecture. The speech recognizer …

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