Peter E. Hart

A Formal Basis for the Heuristic Determination of Minimum Cost Paths

Although the problem of determining the minimum cost path through a graph arises naturally in a number of interesting applications, there has been no underlying theory to guide the development of efficient search procedures. Moreover, there is no adequate conceptual framework within which the various ad hoc search strategies proposed to date can be compared. This paper describes how heuristic information from the problem domain can be incorporated into a formal mathematical theory of graph searching and demonstrates an optimality property of a class of search strategies.

Use of the Hough transformation to detect lines and curves in pictures

Hough has proposed an interesting and computationally efficient procedure for detecting lines in pictures. This paper points out that the use of angle-radius rather than slope-intercept parameters simplifies the computation further. It also shows how the method can be used for more general curve fitting, and gives alternative interpretations that explain the source of its efficiency.

Subjective bayesian methods for rule-based inference systems

The general problem of drawing inferences from uncertain or incomplete evidence has invited a variety of technical approaches, some mathematically rigorous and some largely informal and intuitive. Most current inference systems in artificial intelligence have emphasized intuitive methods, because the absence of adequate statistical samples forces a reliance on the subjective judgment of human experts. We describe in this paper a subjective Bayesian inference method that realizes some of the advantages of both formal and informal approaches. Of particular interest are the modifications needed to deal with the inconsistencies usually found in collections of subjective statements.

MODEL DESIGN IN THE PROSPECTOR CONSULTANT SYSTEM FOR MINERAL EXPLORATION

Prospector is a computer consultant system intended to aid geologists in evaluating the favorability of an exploration site or region for occurrences of ore deposits of particular types. Knowledge about a particular type of ore deposit is encoded in a computational model representing observable geological features and the relative significance thereof. We describe the form of models in Prospector, focussing on inference networks of geological assertions and the Bayesian propagation formalism used to represent the judgmental reasoning process of the economic geologist who serves as model designer. Following the initial design of a model, simple performance evaluation techniques are used to assess the extent to which the performance of the model reflects faithfully the intent of the model designer. These results identify specific portions of the model that might benefit from “fine tuning”, and establish priorities for such revisions. This description of the Prospector system and the model design process serves to illustrate the process of transferring human expertise about a subjective domain into a mechanical realization.

Correction to "A Formal Basis for the Heuristic Determination of Minimum Cost Paths"

Our paper on the use of heuristic information in graph searching defined a path-finding algorithm, A*, and proved that it had two important properties. In the notation of the paper, we proved that if the heuristic function ñ (n) is a lower bound on the true minimal cost from node n to a goal node, then A* is <u>admissible;</u> i.e., it would find a minimal cost path if any path to a goal node existed. Further, we proved that if the heuristic function also satisfied something called the <u>consistency assumption,</u> then A* was <u>optimal;</u> i.e., it expanded no more nodes than any other admissible algorithm A no more informed than A*. These results were summarized in a book by one of us.

Directions for AI in the eighties

The 1980s will be an exciting decade for artificial intelligence, one in which we can expect to see considerable progress on scientific questions, widespread application of Al techniques to problems of practical significance, and major changes in the social, political and economic structure of the field. In this article, I will attempt to identify some of the commercial, scientific and sociological considerations that I think will be important in coming years. In particular, I will introduce the metaphor of deep versus surface systems, and pose some challenges arising from the recognition of this distinction.

Query-free information retrieval

To liberate users from burdensome information-retrieval activities while incurring minimal system-development and runtime costs, the authors present query-free information retrieval. Their system, Fixit, integrates an expert diagnostic system with a preexisting full-text database of maintenance manuals.

Document image database retrieval and browsing using texture analysis

A system is presented that uses texture to retrieve and browse images stored in a large document image database. A method of graphically generating a candidate search image is used that shows the visual layout and content of a target document. All images similar to this candidate are returned for the purpose of browsing or further query. The system is accessed using a World Wide Web (Web) browser. Applications include the retrieval and browsing of document images including newspapers, fares and business letters.

A functional approach to integrating database and expert systems

A new system architecture shares certain characteristics with database systems, expert systems, functional programming languages, and spreadsheet systems, but is very different from any of these.

Document analysis techniques for the infinite memory multifunction machine

A system that saves a digital copy of every document that users copy, print, or fax, without asking the user, has recently been proposed. Referred to as the Infinite Memory Multifunction Machine (IM/sup 3/), this system solves most of the problem of lost documents. However, because of the indiscriminate way it captures data, it is important that users have easy-to-use retrieval tools. Two document analysis techniques are described that simplify retrieval from large collections like the IM/sup 3/. One technique detects duplicates or versions of a document. Another method automatically files a document in a hierarchy familiar to a user. Experimental results are presented that illustrate the performance of each method.