Inconsistency Robustness in Logic Programs

Abstract

Inconsistency robustness is "information system performance in the face of continually pervasive inconsistencies." A fundamental principle of Inconsistency Robustness is to make contradictions explicit so that arguments for and against propositions can be formalized. This paper explores the role of Inconsistency Robustness in the history and theory of Logic Programs. Robert Kowalski put forward a bold thesis: "Looking back on our early discoveries, I value most the discovery that computation could be subsumed by deduction." However, mathematical logic cannot always infer computational steps because computational systems make use of arbitration for determining which message is processed next by a recipient that is sent multiple messages concurrently. Since reception orders are in general indeterminate, they cannot be inferred from prior information by mathematical logic alone. Therefore mathematical logic cannot in general implement computation. Over the course of history, the term "Functional Program" has grown more precise and technical as the field has matured. "Logic Program" should be on a similar trajectory. Accordingly, "Logic Program" should have a general precise characterization. In the fall of 1972, different characterizations of Logic Programs that have continued to this day: * A Logic Program uses Horn-Clause syntax for forward and backward chaining * Each computational step (according to Actor Model) of a Logic Program is deductively inferred (e.g. in Direct Logic). The above examples are illustrative of how issues of inconsistency robustness have repeatedly arisen in Logic Programs.