In a large distributed system spanning many administrative domains such as a Data Grid, it is desirable to maintain and query dynamic and timely information about active participants such as services, resources and user communities. However, in such a database system, the set of information tuples in the universe is partitioned over many distributed nodes, for reasons including autonomy, scalability, availability, performance and security. It is not obvious how to enable general-purpose

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... y query support and collective collaborative functionality that operate on the distributed system as a whole, rather than on a given part of it. Further, it is not obvious how to allow for search results that are fresh, allowing dynamic content. It appears that a Peer-to-Peer (P2P) database network may be well suited to support dynamic distributed database search, for example for service discovery. In this paper, we devise the Unified Peer-to-Peer Database Framework (UPDF), which allows to express specific applications for arbitrary query languages (e.g. XQuery, SQL) and node topologies, and a wide range of data types, query response modes (e.g. Routed, Direct and Referral Response), neighbor selection policies, pipelining characteristics, timeout and other scope options.