Showing papers by "Brian C. Williams published in 1986"

Doing time: putting qualitative reasoning on firmer ground

Abstract: Recent work in qualitative reasoning has focused on predicting the dynamic behavior of continuous physical systems. Significant headway has been made in identifying the principles necessary to predict this class of behavior. However, the predictive inference engines based on these principles are limited in their ability to reason about time. This paper presents a general approach to behavioral prediction which overcomes many of these limitations. Generality results from a clean separation between principles relating to time, continuity, and qualitative representations. The resulting inference mechanism, based on propagation of constraints, is applicable to a wide class of physical systems exhibiting discrete or continuous behavior, and can be used with a variety of representations (e.g., digital, quantitative, qualitative or symbolic abstractions). In addition, it provides a framework in which to explore a broad range of tasks including prediction, explanation, diagnosis, and design.

Reasoning about multiple faults

Abstract: Diagnostic tasks require determining the differences between a model of an artifact and the artifact itself. The differences between the manifested behavior of the artifact and the predicted behavior of the model guide the search for the differences between the artifact and its model. The diagnostic procedure presented in this paper is model-based, inferring the behavior of the composite device from knowledge of the structure and function of the individual components comprising the device. The system (GDE — General Diagnostic Engine) has been implemented and tested on examples in the domain of troubleshooting digital circuits. This research makes several novel contributions: First, the system diagnoses failures due to multiple faults. Second, failure candidates are represented and manipulated in terms of minimal sets of violated assumptions, resulting in an efficient diagnostic procedure. Third, the diagnostic procedure is incremental, reflecting the iterative nature of diagnosis. Finally, a clear separation is drawn between diagnosis and behavior prediction, resulting in a domain (and inference procedure) independent diagnostic procedure.

Back to backtracking: controlling the ATMS

Abstract: The ATMS (Assumption-Based Truth Maintenance System) provides a very general facility for all types of default reasoning. One of the principal advantages of the ATMS is that all of the possible (usually mutually inconsistent) solutions or partial solutions are directly available to the problem solver. By exploiting this capability of the ATMS, the problem solver can efficiently work on all solutions simultaneously and avoid the computational expense of backtracking. However, for some applications this ATMS capability is more of a hindrance than a help and some form of backtracking is necessary. This paper first outlines some of the reasons why backtracking is still necessary, and presents a powerful backtracking algorithm which we have implemented which backtracks more efficiently than other approaches.