In short: 
Views in peer-to-peer

ViP2P is a fully functional Java-based platform for the efficient, scalable management of XML documents in structured peer-to-peer networks based on distributed hash table (DHT) indices. We exploit indices (or materialized views) deployed in the P2P network independently by the peers, to answer an interesting dialect of tree pattern queries. There is a query (and view) language, a rewriting algorithm, view definition indexing strategies based on the DHT and much more...

Ioana Manolescu