XML data integration in peer-to-peer data management systems

P2P systems are commonly accepted as an efficient means of sharing data among large, diverse and dynamic set of users. Nowadays sharing data imposes new challenges in P2P systems concerning supporting advanced querying beyond simple keyword-based retrieval. We assume that each peer stores schema of its local data, mappings to some other peers, and schema constraints (functional dependencies). The goal of the integration is to answer queries formulated against arbitrarily chosen peers. The answer consists of data stored in the queried peer as well as data of its direct and indirect acquaintances. We focus on the problem of query propagation and merging partial answers in such environment. We show how XML functional dependencies defined over schemas, determine the selection of the merging mode of partial answers to increase information content of the answer by recovering some missing values. We show how the discussed method has been implemented in SixP2P system (Semantic Integration of XML data in P2P environment).