A step towards incremental maintenance of the composed schema mapping

Schema mapping plays a fundamental role in modern information systems. Mapping composition is an operator that combines a chain of successive schema mappings into a single schema mapping. By pre-computing the composed schema mapping, the system can achieve significant performance benefits. However, when a change occurs on any mapping in the chain, the composed schema mapping has to be maintained correspondingly. In this paper we consider a restricted form of the problem in the XML setting and propose an incremental maintenance approach. Specifically, given a chain of successive mappings, we transform intermediately them into trees that consist of atomic rules and then divide the composition into sub-compositions of the atomic rules. The dividing composition approach provides a fine-grained perspective of the composition relationships between the mappings. We depict such information through an auxiliary data structure called composition relationship graph (CRG). When changes occur on any mapping in the chain, the corresponding maintenance algorithms are developed based on the dividing approach and the CRG, which compute the changes on the composed mapping and then repair it into the new version, such that the computation involves only the atomic rules that are relevant with the maintenance. We evaluate our maintenance approach and report the first experiments results, which show that it is efficient.