Walter Hamscher

KER Journal 1992 Journal Article

Model-based reasoning in financial domains

• Walter Hamscher

Abstract Finance is a challenging yet appropriate domain for model-based reasoning, an area of research otherwise grounded in classical physics. Among the many features that suggest a model-based approach are that firms have formal internal structures, business entities have idealizable behaviours, and there is a history of formal analysis of business problems. This article discusses the motivations and foundations of the model-based approach, and surveys several existing artificial intelligence programs that exploit its advantages. The survey shows that there are ample opportunities for useful systems and significant research in this area. However, accomplishing either of these goals depends crucially upon moving beyond qualitative models based only on accounting information, which tend not to capture the actual complexities of the domain.

AAAI Conference 1992 Conference Paper

Modeling Accounting Systems to Support Multiple Tasks: A Progress Report

• Walter Hamscher

A domain model in SAVILE represents the steps involved in producing and processing financial data in a company, using an ontology appropriate for several reasoning tasks in accounting and auditing. SAVILE is an implemented program that demonstrates the adequacy and appropriateness of this ontology of financial data processing for evaluating internal controls, designing tests, and other audit planning related tasks. This paper discusses the rationale, syntax, semantics, and implementation of the ontology as it stands today.

AAAI Conference 1991 Conference Paper

ACP: Reason Maintenance and Inference Control for Constraint Propagation Over Intervals

• Walter Hamscher

AAAI Conference 1984 Conference Paper

Diagnosing Circuits With State: An Inherently Underconstrained Problem

• Walter Hamscher

Hard problems can be hard because they are computationally intractable, or because they are underconstrained. Here we describe candidate generation for digital devices with state, a fault localization problem that is intractable when the devices are described at low levels of abstraction, and is underconstrained when described at higher levels of abstraction. Previous work [l] has shown that a fault in a combinatorial digital circuit can be localized using a constraint-based representation of structure and behavior. ln this paper we (1) extend this representation to model a circuit with state by choosing a time granularity and vocabulary of signals appropriate to that circuit; (2) demonstrate that the same candidate generation procedure that works for combinatorial circuits becomes indiscriminate when applied to a state circuit modeled in that extended representation;(3) show how the common technique of single-stepping can be viewed as a divide-and-conquer approach to overcoming that lack of constraint; and (4) illustrate how using structural detail can help to make the candidate generator discriminating once again, but only at great cost.

AAAI Conference 1983 Conference Paper

Using Structural and Functional Information in Diagnostic Design

• Walter Hamscher

We wish to design a diagnostic for a device from knowledge of its structure and function. The diagnostic should achieve both coverage of the faults that can occur in the device, and should strive to achieve specificify in its diagnosis when it detects a fault. A system is described that uses a simple model of hardware structure and function, representing the device in terms of its internal primitive functions and connections. The system designs a diagnostic in three steps. First, an extension of path sensitization is used to design a test for each of the connections in the device. Next, the resulting tests are improved by increasing their specificity. Finally the tests are ordered so that each relies on the fewest possible connections. We describe an implementation of the first of these steps and show an example of the results for a simple device.

AAAI Conference 1982 Conference Paper

Diagnosis Based on Description of Structure and Function

• Randall Davis
• Walter Hamscher
• Mark Shirley

While expert systems have traditionally been built using large coliections of rules based on empirlcal associations, interest has grown recently in the use of systems that reason from representations of structure and function. Our work explores the use of such models in troubleshooting digital electronics. We describe our work to date on (i) a language for describing structure, (ii) a language for describing function, and (i/i) a set of prlnctples for troubleshooting that uses the two descriptions to guide its investigation. In discussing troubleshooting we show why the traditional approach --- test generation --- solves a different [JrdJklll dnti vve &SCllSS a Ilumber of its pIdC, hd ShOrt~Olllill~S. We consider next the style of debugging known as violated expectations and demonstrate why it is a fundclmental advance over traditional test generation. Further exploration of this approach. however, demonstrates that it is incapable of dealing with commonly known classes of faults. We explain the shortcoming as arisirlg from the use of a fault model that is both implicit and inseparable from the basic troubleshooting metl~odology. We argue for the importance of fault models that are explicit, separated from the troubleshooting mechanism, and retractable in much the same sense that inferences are retracted in current systems.