Linguistic Processing in a Speech Understanding System

The goal of a speech understanding system is to correctly identify the action to be taken as a response to a user’s voiced request. To this purpose, the system has to rely on some type of linguistic knowledge beside merely recognize words. Several approaches have been proposed to employ language modeling in speech understanding. They include unified architectures integrating modular knowledge sources that account for every level of knowledge from acoustics to linguistics, and two-level architectures in which the separation between recognition and linguistic processing is well defined. Within this approach, two main methods may be conceived: linguistic constraints are integrated into the recognizer, which decodes one string of words that is treated by a natural language interface; or the recognizer produces a scored word lattice that is subsequently processed by a suitable linguistic module. For the present study, this latter approach was considered the most promising one, provided a satisfactory solution to efficient word lattice parsing could be found.