Towards an automated directory information system

This paper describes a design and feasibility study for a large-scale automatic directory information system with a scalable architecture. The current demonstrator, called PADIS-XL, operates in realtime and handles a database of a medium-size German city with 130,000 listings. The system uses a new technique of taking a combined decision on the joint probability over multiple dialogue turns, and a dialogue strategy that strives to restrict the search space more and more with every dialogue turn. During the course of the dialogue, the last name of the desired subscriber must be spelled out. The spelling recognizer permits continuous spelling and uses a context-free grammar to parse common spelling expressions. This paper describes the system architecture, our maximum a-posteriori (MAP) decision rule, the spelling grammar, and the dialogue strategy. We give results on the SPEECHDAT and SIETILL databases on recognition of first names by spelling and on jointly deciding on the spelled and the spoken name. In a 35,000-names setup, the joint decision reduced name-recognition errors by 31%.