An Extensible Framework for Repairing Constraint Violations

In this paper we describe a new approach to repairing violations of integrity constraints in databases with null values. By adopting basic concepts from model-based diagnosis, we show how simultaneous reasons for violations of (di erent) constraints can be determined. These reasons, represented as sets of facts, directly indicate possible repair actions that guarantee to remove the observed violations. By interleaving the diagnosis of constraint violations and the execution of repair actions, we draw an enumeration schema for possible minimal repair transactions as sequences of repair actions. Each such transaction, when applied to the inconsistent database, guarantees to result in a database consistent with all constraints. In order to enumerate possible repair transactions, repair actions are performed hypothetically using auxiliary relations. This enables the user to query intermediate as well as result states obtained by di erent repairs in advance. In order to provide a suitable front-end to the general enumeration schema, we describe various repair strategies which can be imposed by the user. These strategies follow individually speci ed repair goals and can easily be integrated into the enumeration schema for repair transactions. The proposed strategies range from aspects of minimal change over priorities of stored facts up to the user interaction with the repair process.