This book presents a query translation mechanism between heterogeneous peers in Peer to Peer Database Networks. A Peer to Peer Database Network combines a database management system with P2P functionality. In a such a network, each peer chooses its own data model and schema, and maintains data independently without any global coordinator. One of the problems in such a system is translating queries between peers taking into account both the schema and data heterogeneity. Query translation is the problem of rewriting a query posed in terms of one peer schema to a query in terms of another peer...