Robust Translation of Spontaneous Speech: A Multi-Engine Approach

Verbmobil is a speaker-independent and bidirectional speech-to-speech translation system for spontaneous dialogs that can be accessed via GSM mobile phones. It handles dialogs in three business-oriented domains, with context-sensitive translation between four languages (English, German, Japanese, and Chinese). We show that in Verbmobil's multi-blackboard and multi-engine architecture the results of concurrent processing threads can be combined in an incremental fashion. We argue that all results of concurrent processing modules must come with a confidence value, so that statistically trained selection modules can choose the most promising result. Packed representations together with formalisms for underspecification capture the uncertainties in each processing phase, so that the uncertainties can be reduced by linguistic, discourse and domain constraints as soon as they become applicable. Distinguishing features like the multilingual prosody module and the generation of dialog summaries are highlighted. We conclude that Verbmobil has successfully met the project goals with more than 80% of approximately correct translations and a 90% success rate for dialog tasks. One of the main lessons learned from the Verbmobil project is that the problem of speech-tospeech translation can only be cracked by the combined muscle of deep and shallow processing approaches.