Query Decomposition Strategy for Integration of Semistructured Data

Data integration systems provide a unified view of various sources of data distributed over the wide-area networks. User requests issued at a central site must be decomposed into a number of sub-requests, that are later on processed at the remote sites. The results are integrated at a central site and returned to a user. A decomposition strategy of global user requests and scheduling of sub-requests at a central site has a significant impact on performance of data integration process. This paper proposes an efficient decomposition strategy for the systems that integrate semistructured data. We define a new system of operations on XML documents to represent XQuery user requests and the results of decompositions of such requests. A cost-based optimisation is used to find the optimal size of sub-requests and their optimal scheduling at a central site.