The book "Expressive Query Translation in Peer Database Networks" offers a comprehensive examination of a mechanism for query translation between heterogeneous peers in peer-to-peer database networks. In such networks, each peer combines a database management system with P2P functionalities and independently chooses its own data model and schema. This leads to challenges in query translation, as schema and data heterogeneity must be taken into account. The author, Muhammad M. Masud, presents an innovative approach based on user-specific syntax and data-level mappings created by each peer and shared with other peers. By applying translation rules based on this mapping information, effective query translation is made possible. The book evaluates the mechanism using a prototype of a peer-to-peer network to demonstrate the practicality of the approach.