A scheme for syntax-directed translation that mirrors compositional model-theoretic semantics is discussed. The scheme is the basis for an English translation system called PATR and was used to specify a semantically interesting fragment of English, including such constructs as tense, aspect, modals, and various lexically controlled verb complement structures. PATR was embedded in a question-answering system that replied appropriately to questions requiring the computation of logical entailments.

We have introduced the notion of the closed world assumption for deductive question-answering. This says, in effect, "Every positive statement that you don't know to be true may be assumed false". We have then shown how query evaluation under the closed world assumption reduces to the usual first order proof theoretic approach to query evaluation as applied to atomic queries. Finally, we have shown that consistent Horn data bases remain consistent under the closed world assumption and that definite data bases are consistent with the closed world assumption. ACKNOWLEDGMENT This paper was written with the financial support of the National Research Council of Canada under grant A7642. Much of this research was done while the author was visiting at Bolt, Beranek and Newman, Inc., Cambridge, Mass. I wish to thank Craig Bishop for his careful criticism of an earlier draft of this paper.

This article examines the process of specifying a question-answering help facility in the context of UNIX mail. The specification was based upon experimental expert-user facilitative dialogues. These dialogues were analyzed using a classification scheme developed for the purpose. The scheme provides a metalanguage for describing patterns of intent and rhetorical structure in dialogue. Using the scheme as a tool, common patterns in expert-user dialogue emerged, providing insights into both tutoring strategy and the linguistic forms required to generate help output.

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Session 6 Logic: II Theorem Proving and STEPS TOWARD AUTOMATIC THEORY FORMATION John Seely Brown Information and Computer Science Department University of California Irvine Irvine, California Abstract This paper describes a theory formation system which can discover a partial axiomization of a data base represented as extensionally defined binary relations.- The system first discovers all possible intensional definitions of each binary relation in terms of the others. It then determines a minimal set of these relations from which the others can be defined. It then attempts to discover all the ways the relations of this minimal set can interact with each other, thus generating a set of inference rules. Although the system was originally designed to explore automatic techniques for theory construction for question-answering systems, it is currently being expanded to function as a symbiotic system to help social scientists explore certain kinds of data bases. Introduction For over a decade researchers in AI have been designing question-answering systems which are capable of deriving "implicit" facts from a sparse data base.

In one major section we discuss the imprecision, the incompleteness, the openendedness, and the uncertainty of people's knowledge. In the other major section we discuss strategies people use to make different types of deductive, negative, and functional inferences, and the way uncertainties combine in these inferences. Keywords Semantics, inference, cognitive processes, natural language processing, human memory, question-answering systems, deduction, analogy 1. Introduction In this paper we will discuss how to represent and process information in a computer in ways that are natural to people. This does not mean doing away completely with representations and procedures which computers have traditionally used, but adding new representations and procedures which they have not used. People often store and communicate imprecise, incomplete, and unquantified information; they often assert truth or falsity in relative terms; and they seldom seem to use rigorous logic in their inferential processes. Because of these conditions, people seem to have an almost infinite information processing capacity, with inference making and problem solving abilities more refined and far more flexible than any existing computer program. How can we study these human capabilities in order to make our machines show similar performance? A combination of approaches is perhaps best. Observation of people's behavior, introspection, some experimentation, protocol analysis, and synthesis of computer programs can all be valuable techniques.

MENTAL can be used as a guestion-answering system with formatted input /output, as a vehicle for experimenting with various theories of semantic structures or as the memory management portion of a natural language question-answering system. 1. Introduction In order to develop machines capable of "understanding" natural language, it is extremely valuable, if not necessary, to design a method of organizing a corpus of data to facilitate the storage and retrieval of information on many subjects, some in depth, some in breadth; to facilitate the storage, retrieval and use of the many complex relationships among real-world concepts; to facilitate the storage, retrieval and use of information which tells how other information in the corpus may be used to further explicate implied relationships among concepts; and to facilitate the identification from the vast corpus of data of those pieces of information most directly relevant to any given topic. This paper describes a data structure (MENS) and procedures for manipulating it The research reported herein was partially supported by a grant from the National Science Foundation (GJ-583) and partially by USAF Proj.

Kuhn (1962) has persuasively argued that science progresses by means of its paradigms--its models of the general nature of a research area--and that at the frontiers of research the primary quest is for a good paradigm. The small frontier outpost of language data processing has been characterized by an intensive seeking for a paradigm suitable to guide its researchers as they survey the complex topography of natural language structures. The earliest paradigm--one that led mechanical translators and early information retrievalists into a hopeless cul-de-sac--was that words (i.e.

A question-answering system. Tech. Note 15, AI Group, Stanford Research Institute, Menlo Park, Calif.

This paper shows how a question-answering system can be constructed usingfirst-order logic as its language and a resolution-type theorem-prover as itsdeductive mechanism. A working computer-program, Q A3, based on theseideas is described. The performance of the program compares favorably withseveral other general question-answering systems.Reprinted in B. L. Webber and N. J. Nilsson (eds.), Readings in Artificial Intelligence, pp, 202-222, San Francisco: Morgan Kaufmann, 1981 Machine Intelligence 4, pp. 183-205 Meltzer, B. and Michie, D.(eds.). Edinburgh: Edinburgh University Press.