THE PHILIPS AUTOMATIC TRAIN TIMETABLE INFORMATION-SYSTEM

In this article, we describe an automatic system for train timetable i nformation over the telephone that provides accurate connections betwe en 1200 German cities. The caller can talk to it in unrestricted, natu ral, and fluent speech, very much like he or she would communicate wit h a human operator, and is not given any instructions in advance. The system's four main components, speech recognition, speech understandin g, dialogue control, and speech output, are separated into independent modules that are executed sequentially. Word graphs form the interfac e between recognition and understanding; an attributed stochastic cont ext-free grammar is then used to determine the meaning of a spoken sen tence. 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, t hen the telephone number was passed around within the department, the company and, finally, the outside world. After each step, the newly co llected material was used for retraining, as well as for general impro vements.