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A sophisticated natural language system requires a large knowledge base. A methodology is described for constructing one in a principled way. Facts are selected for the knowledge base by determining what facts are linguistically presupposed by a text in the domain of interest. The facts are sorted into clnsters, and within each cluster they are organized according to their logical dependencies. Finally, the facts are encoded as predicate calculus axioms. | Building a Large Knowledge Base for a Natural Language System Jerry R. Hobbs Artificial Intelligence Center SRI International and Center for the Study of Language and Information Stanford University Abstract A sophisticated natural language system requires a large knowledge base. A methodology is described for constructing one in a principled way. Facts are selected for the knowledge base by determining what facts are linguistically presupposed by a text in the domain of interest. The facts are sorted into clusters and within each cluster they are organized according to their logical dependencies. Finally the facts are encoded as predicate calculus axioms. 1. The Problem1 It is well-known that the interpretation of natural language discourse can require arbitrarily detailed world knowledge and that a sophisticated natural language system must have a large knowledge base. But heretofore the knowledge bases in natural language systems have either encoded only a few kinds of knowledge - e.g. sort hierarchies - or facts in only very narrow domains. The aim of this paper is to present a methodology for constructing an intermediate-size knowledge base for a natural language system which constitutes a manageable and principled midway point between these simple knowledge bases and the impossibly detailed knowledge bases that people seem to use. The work described in this paper has been carried out as part of a project to build a system for natural language access to a computerized medical textbook on hepatitis. The user asks a question in English and rather than attempting to answer it the system returns the passages in the text relevant to the question. The English query is translated into a logical form by a syntactic and semantic translation component Grosz et al. 1982 . The textbook is represented by a text structure consisting among other things of summaries of the contents of individual passages expressed in a logical language. Inference procedures making use of a .
