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Classical treatment of consistency violations is to back out a database operation or transaction.In applications with large numbers of fairly complex consistency constraints this clearly is an unsatisfactory solution. Instead, if a violation is detected the user should be given a diagnosis of the constraints that failed, a line of reasoning on the cause that could have led to the violation, and suggestions for a repair. The problem is particularly complicated in a deductive database system where failures may be due to an inferred condition rather than simply a stored fact, but the repair can only be applied to the underlying facts. The paper presents a system which provides automated support in such situations. It concentrates on the concepts and ideas underlying the approach and an appropriate system architecture and user guidance, and sketches some of the heuristics used to gain in performance.

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