The Text System for Natural Language Generation: An Overview

THE TEXT SYSTEM FO~NATURAL LANGUAGE GENERATION: AN OVERVIEW* Kathleen R. M::Keown Dept. of Computer & Information Science The Moore School University of Pennsylvania Philadelphia, Pa. 19104 ABSTRACT Computer-based generation of natural language requires consideration of two different types of problems: i) determining the content and textual shape of what is to be said, and 2) transforming that message into English. A computational solution to the problems of deciding what to say and how to organize it effectively is proposed that relies on an interaction between structural and semantic processes. Schemas, which encode aspects of discourse structure, are used to guide the generation process. A focusing mechanism monitors the use of the schemas, providing constraints on what can be said at any point. These mechanisms have been implemented as part of a generation method within the context of a natural language database system, addressing the specific problem of responding to questions about database structure. 1.0 INTRODUCTION Deciding what to say and how to organize it effectively are two issues of particular importance to the generation of natural language text. In the past, researchers have concentrated on local issues concerning the syntactic and lexical choices involved in transforming a pre-determined message into natural language. The research described here ~nphasizes a computational Solution to the more global problems of determining the content and textual shape of what is to be said. ~re specifically, my goals have been the development and application of principles of discourse structure, discourse coherency, and relevancy criterion to the computer generation of text. These principles have been realized in the TEXT system, reported on in this paper. The main features of the generation method used in TEXT include I) an ability to select relevant information, 2) a system for pairing rhetorical techniques (such as analogy) with discourse purv~ses (such as defining terms) and 3) a focusing mec~mnism. Rhetorical techniques, which encode aspects of discourse structure, guide the selection of information for inclusion in the text from a relevant knowledge poq~l - a subset of *This work was partially supported by National Science ~Dundation grant #MCS81-07290. the knowledge base which contains information relevant to the discourse purpose. The focusing mechanism helps maintain discourse coherency. It aids in the organization of the message by constraining the selection of information to be talked about next to that which ties in with the previous discourse in an appropriate way. These processes are described in more detail after setting out the framework of the system. 2.0 APPLICATION In order to test generation principles, the TEXT system was developed as part of a natural language interface to a database system, addressing the specific problem of generating answers to questions about database structure. Three classes of questions have been considered: questions about information available in the database, requests for definitions, and questions about the differences between database entities [MCKE(3WN 80]. In this context, input questions provide the initial motivation for speaking. Although the specific application of answering questions about database structure was used primarily for testing …

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