A Representation for Complex and Evolving Data Dependencies in Generation

A Representation for Complex and Evolving Data Dependencies in Generation C Mellish $, R Evans t, L Cahill t, C Doran t, D Paiva t, M Reape $, D Scott t, N Tipper t tInformation Technology Research Institute, University of Brighton, Lewes Rd, Brighton, UK SDivision of Informatics, University of Edinburgh, 80 South Bridge, Edinburgh, UK rags@itri, brighton, ac. uk http :/www. itri. brighton, ac. uk/proj ect s/rags Abstract This paper introduces an approach to represent- ing the kinds of information that components in a natural language generation (NLG) sys- tem will need to communicate to one another. This information may be partial, may involve more than one level of analysis and may need to include information about the history of a derivation. We present a general representation scheme capable of handling these cases. In ad- dition, we make a proposal for organising inter- module communication in an NLG system by having a central server for this information. We have validated the approach by a reanalysis of an existing NLG system and through a full im- plementation of a runnable specification. 1 Introduction One of the distinctive properties of natural lan- guage generation when compared with other language engineering applications is that it has to take seriously the full range of linguistic rep- resentation, from concepts to morphology, or even phonetics. Any processing system is only as sophisticated as its input allows, so while a natural language understanding system might be judged primarily by its syntactic prowess, even if its attention to semantics, pragmatics and underlying conceptual analysis is minimal, a generation system is only as good as its deep- est linguistic representations. Moreover, any at- tempt to abstract away from individual gener- ation systems to a more generic architectural specification faces an even greater challenge: not only are complex linguistic representations required, able to support the dynamic evolu- tionary development of data during the gener- * Now at the MITRE Corporation, Bedford, MA, USA, cdoran@mitre, org. ation process, but they must do so in a generic and flexible fashion. This paper describes a representation devel- oped to meet these requirements. It offers a formally well-defined declarative representation language, which provides a framework for ex- pressing the complex and dynamic data require- ments of NLG systems. The approach supports different levels of representation, mixed repre- sentations that cut across levels, partial and shared structures and 'canned' representations, as well as dynamic relationships between data at different stages in processing. We are using the approach to develop a high level data model for NLG systems as part of a generic generation architecture called RAGS 1. The framework has been implemented in the form of a database server for modular genera- tion systems. As proof of concept of the frame- work, we have reimplemented an existing NLG system. The system we chose was the Caption Generation System (CGS) (Mittal et al., 1995; Mittal et al., 1998). The reimplementation in- volved defining the interfaces to the modules of CGS in terms of the …

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