The Philips automatic train timetable information system

Abstract

In this article, we describe an automatic system for train timetable information over the telephone that provides accurate connections between 1200 German cities. The caller can talk to it in unrestricted, natural, and fluent speech, very much like he or she would communicate with a human operator, and is not given any instructions in advance. The system's four main components, speech recognition, speech understanding, dialogue control, and speech output, are separated into independent modules that are executed sequentially. Word graphs form the interface between recognition and understanding; an atttributed stochastic context-free grammar is then used to determine the meaning of a spoken sentence. In an ongoing field trial, this system has been made available to the general public, both to gather speech data and to evaluate its performance. This field test was organized as a bootstrapping process: initially, the system was trained with just the developers' voices, then the telephone number was passed around within the department, the company and, finally, the outside world. After each step, the newly collected material was used for retraining, as well as for general improvements.