Semantic Overlay Networks

In a handful of years only, Peer-to-Peer (P2P) systems have become an integral part of the Internet. After a few key successes related to music-sharing (e.g., Napster or Gnutella), they rapidly developed and are nowadays firmly established in various contexts, ranging from large-scale content distribution (BitTorrent) to Internet telephony(Skype) or networking platforms (JXTA). The main idea behind P2P is to leverage on the power of end-computers: Instead of relying on central components (e.g., servers), services are powered by decentralized overlay architectures where endcomputers connect to each other dynamically. So far, much effort has been devoted to the development of distributed hashtables (DHTs) to index data in a totally decentralized way. Though extremely robust and scalable, these systems suffer from simplistic data models, which mainly consist of unstructured collections of key-value pairs. More recently however, a significant number of uncorrelated research efforts focused on enriching P2P systems with more expressive data models and query languages. As a result, various Semantic Overlay Networks (SON) supporting relational, semi-structured or triple-based collections of data over decentralized P2P networks started to appear. SON systems can be considered as truly unique as they aim at managing structured data in very large-scale, decentralized, heterogeneous and highly dynamic environments.