Cognitive Science, vol. 3, No. 1, pp. 67-90.

To choose their actions, reasoning programs must be able to make assumptions and subsequently revise their beliefs when discoveries contradict these assumptions. The Truth Maintenance System (TMS) is a problem solver subsystem for performing these functions by recording and maintaining the reasons for program beliefs. Such recorded reasons are useful in constructing explanations of program actions and in guiding the course of action of a problem solver. This paper describes (1) the representations and structure of the TMS, (2) the mechanisms used to revise the current set of beliefs, (3) how dependency-directed backtracking changes the current set of assumptions, (4) techniques for summarizing explanations of beliefs, (5) how to organize problem solvers into "dialectically arguing" modules, (6) how to revise models of the belief systems of others, and (7) methods for embedding control structures in patterns of assumptions. We stress the need of problem solvers to choose between alternative systems of beliefs, and outline a mechanism by which a problem solver can employ rules guiding choices of what to believe, what to want, and what to do.Artificial Intelligence 12(3):231-272

Summary of Stanford Ph.D. dissertation, Computer Science Dept. Stanford University (1977).Artificial Intelligence 12(2): 73-119.

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.

A constraint network representation is presented for a combinatorial search problem: finding values for a set of variables subject to a set of constraints. A theory of consistency levels in such networks is formulated, which is related to problems of backtrack tree search efficiency. An algorithm is developed that can achieve any level of consistency desired, in order to preprocess the problem for subsequent backtrack search, or to function as an alternative to backtrack search by explicitly determining all solutions.

Most resolution theorem provers convert a theorem into clause form before attempting to find a proof. The conventional translation of a first-order formula into clause form often obscures the structure of the formula, and may increase the length of the formula by an exponential amount in the worst case. We present a non-standard clause form translation that preserves more of the structure of the formula than the conventional translation. This new translation also avoids the exponential increase in size which may occur with the standard translation. We show how this idea may be combined with the idea of replacing predicates by their definitions before converting to clause form.

A new system for the analysis of aerial photographs of suburban areas is presented. In this system, regions are characterized by various spectral and spatial features such as brightness, color, size, shape, texture, and spatial relationships with other regions. The analysis proceeds from a global survey of the picture to the detailed analysis of specific regions. The former process extracts several kinds of characteristic regions which are supposed to include specific objects by using knowledge-free picture processing programs. In the detailed analysis, several object-detection programs perform parallel analysis of extracted characteristic regions in detail to recognize objects such as crop fields, woods, roads, and houses.

It can be seen that a great deal of worthwhile material has now been generated about computer chess. There is also quite a bit of nonsense by persons who have never built a program. Several groups with excellent programs have done little publishing, although I can hardly blame them since their work requires much time and is usually unsupported by any funding agencies. Certain staples have given rise to duplication: All but one of the books published explain the depth-first alpha-beta procedure. We expect that by far the largest portion of our readers will be scientists interested in updating their knowledge of the subject.

A model of a text processing package is described which is based on elementary set theory. This is used to describe procedures for computing indexes, concordances, and collocations. Aspects of the implementation of the model are given.