The support for complex queries, such as range, pre?x and aggregation queries, over structured peer-to-peer systems is currently an active and signi?cant topic of research. This paper demonstrates how Skip Tree Graph, as a novel structure, presents an e?cient solution to that problem area through provision of a distributed search tree functionality on decentralised and dynamic environments. Since Skip Tree Graph is based on skip trees, a concurrent approach to skip lists, it constitutes an augmentation of skip graphs that extends its functionality and allows for important performance improvements. This work presents a thorough comparison between these two related peer-to-peer overlay networks, their construction, search algorithms and properties. Being based on tree structures, skip tree graphs supports aggregation queries and multicast/broadcast operations, which cannot be directly implemented in its predecessor. The repair mechanism for healing the structure in case of failures is more e?cient and harnesses the parallelism inherent in P2P networks. Particular consideration is given to the performance of di?erent range-query schemes over the two related structures. Theoretical and experimental results conclude that Skip Tree Graphs outperform skip graphs on both exact-match and range searches. 2007 Elsevier B.V. All rights reserved.
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