Consistent Query Answers in Virtual Data Integration Systems

When data sources are virtually integrated there is no common and centralized mechanism for maintaining global consistency. In consequence, it is likely that inconsistencies with respect to certain global integrity constraints (ICs) will occur. In this chapter we consider the problem of defining and computing those answers that are consistent wrt the global ICs when global queries are posed to virtual data integration systems whose sources are specified following the local-as-view approach. The solution is based on a specification using logic programs with stable model semantics of the minimal legal instances of the integration system. Apart from being useful for computing consistent answers, the specification can be used to compute the certain answers to monotone queries, and minimal answers to non monotone queries.