1 Efficient Maintenance Ofmaterialized

Integrating data and knowledge from multiple heterogeneous sources-like databases, knowledge bases or speciic software packages-is often required for answering certain queries. Recently, a powerful framework for deening mediated views spanning multiple knowledge bases by a set of constrained rules was proposed 26, 4, 17]. We investigate the materialization of these views by unfolding the view deenition and the eecient maintenance of the resulting materialized mediated view in case of updates. Thereby, we consider two kinds of updates: updates to the view and updates to the underlying sources. For each of these two cases several eecient algorithms maintaining materialized mediated views are given. We improve on previous algorithms like the DRed algorithm 13] and introduce a new xpoint operator WP which | opposed to the standard xpoint operator TP 10] | allows us to correctly capture the update's semantics without any recomputation of the materialized view.