Advanced knowledge base debugging for Rulelog

We present a novel approach to debugging expressively rich knowledge representation and reasoning (KRR) logic Rulelog. Rulelog is an extended form of declarative logic programs (LP) under the wellfounded semantics, which allows higher-order logic formulas as axioms in combination with defeasibility mechanisms that include rule cancellation and priorities, along with default and explicit negation. Rulelog also supports strong knowledge interchange with all current major semantic web standards for logical KRR. Rulelog has been implemented in Flora-2 and Silk, both on top of XSB; and (less completely) in Cyc. The debugging approach described here is part of an integrated development environment, most fully implemented in Silk. The approach includes: reasoning trace analysis, based on tabled LP inferencing tables and forestlog; and justification graphs, which treat why-not and defeasibility as well as provenance. The reasoning trace analysis treats performance and runaway computations, including non-termination as well as classic subgoal-ordering issues that arise in database query optimization. Non-termination can be prevented entirely by leveraging the restraint (bounded rationality) feature of Rulelog. Revision/authoring of knowledge is interactive, based on a rapid edit-test-inspect loop and incremental truth maintenance.