Bidirectional use of knowledge in the multi-modal NL access system XTRA

The acceptability and effectiveness of an expert system is critically dependent on its user interface. Natural language could be a well-suited communicative medium; however, current NL interfaces to expert systems show an impeding number of shortcomings. In this paper, it is shown how the XTRA system - a German NL interface between a user and one of various expert systems - employs a framework of novel AI techniques to overcome these shortcomings: it uses various highly interacting knowledge sources for domain-independent linguistic knowledge and for domain-specific world knowledge. This supports the view of NL as a universal communicative medium. In order to allow for a communicatively adequate dialog processing, knowledge sources are bidircctionaly used by both the analysis and the generation component. Both are enhanced with knowledge about the visual context of the dialog situation and about the capability to perform pointing gestures. SB-ONE - a knowledge representation formalism especially tailored for NL processing - deals with these types of knowledge. Together with some important tools of this formalism it constitutes the core of the system, whose performance is demonstrated with the help of an example dialog.