The Use of a Commercial Natural Language Interface in the ATIS Task

A natural language interface for relational databases has been utilized at AT&T Bell Laboratories as the natural language component of the DARPA ATIS common task. This is a part of a larger project that consists of incorporating a natural language component into the Bell Laboratories Speech Recognizer. The commercially available system used in this project was developed by Natural Language Incorporation (NLI), in particular by J. Ginsparg [Ginsparg, 1976]. We relate our experience in adapting the NLI interface to handle domain dependent ATIS queries. The results of this allowed the exploration of several important issues in speech and natural language: 1. the feasabilitiy of using an off-the-shelf commercial product for a language understanding front end to a speech recognizer, 2. the constraints of using a general-purpose product for a specific task. 1 I n t r o d u c t i o n The ATIS common task was designed by DARPA and the members of the DARPA community to build and evaluate a system capable of handling continuous and spontaneous speech recognition as well as natural language understanding. Although the evaluation task is still not fully defined, the ATIS common task presents the opportunity to develop reliable and measurable criteria. The present paper focuses on the natural language component only, the integration with speech being reported in other papers [Pieraccini and Levin, 1991]. The domain of the task is on the Air Travel Information Service (ATIS). The project touches on a wide range of issues both in natural language and speech recognition, including incorporation of an NL interface in speech understanding, flexibility in the type of input language (i.e. spoken or written), relational databases, evaluation of system performance, possible limitations, and others. The NLI system 1 is driven by a syntactic parser designed to handle English queries that are characteristic of the written language. In contrast, ATIS syntax is characteristic of spoken and spontaneous language. Therefore, one of the primary questions in using the NLI system has been how to overcome problems related to the discrepancy between written and spoken language input. Issues related to the ATIS domain and queries on the one hand, and to the construction of the NLI interface on the other hand are addressed. The task of the experiment is then described along with the results. 2 W h y use a c o m m e r c i a l product? Using a commercial product is attractive for a number of reasons: within Bell Laboratories, there has been no effort so far to develop a natural language interface (although this may change). Therefore, it is a significant savings of time and effort to use a publicly available system in order to achieve the larger task, that is the integration of speech and natural language. within the task of language understanding, the use of a natural language interface meant to understand written language input, exposes issues specific to speech incorporation. 3 NLI s y s t e m d e s c r i p t i o n The NLI system is composed of a series of modules, including a spelling corrector, a parser, a semantic interface consulting a knowledge representation base, a con1The acronym NLI should not be confused with the suffix of the transcription sentences ".rdi", meaning natural language input.