PADIS - AN AUTOMATIC TELEPHONE SWITCHBOARD AND DIRECTORY INFORMATION-SYSTEM

The Philips automatic telephone switchboard and directory information system PADIS provides a natural-language user interface to a telephone directory database. Using speech recognition and language understandi ng technologies, the system offers phone numbers, fax numbers, e-mail addresses, and room numbers as well as direct call completion to a des ired party. In this paper, we present the underlying probabilistic fra mework, the system architecture, and the individual modules for speech recognition, language understanding, dialogue control, and speech out put. In addition, we report results on performance and user behaviour obtained from a field test in our research lab with a 600-entry databa se. We derive a new maximum-a-posteriori decision rule which incorpora tes database knowledge and dialogue history as constraints in speech r ecognition and language understanding. It has improved speech understa nding accuracy by 19% (in terms of concept error rate), and reduced at tribute substitution errors (e.g. recognition of a wrong name) by 38%. The decision rule is implemented in a multi-stage approach as a combi nation of state-of-the-art speech recognition, partial parsing with an attributed stochastic context-free grammar, and an N-best algorithm w hich is also described in this paper. The system conducts a flexible m ixed-initiative dialogue rather than using a rigid form-filling scheme , and incorporates database knowledge to optimize the dialogue flow. ( C) 1997 Elsevier Science B.V.