What is Structured P2P Network

During the last years, there was a growing interest in peer-to-peer (P2P) systems, mainly because they fit a wide number of real-life ICT applications. Digital libraries are only a significant instance of P2P systems, but it is very easy to foresee how large the impact of P2P systems on innovative and emerging ICT scenarios, such as e-government and e-procurement, will be during the next years. P2P networks are natively built on top of a very large repository of data objects (e.g., files) that is intrinsically distributed, fragmented, and partitioned among participant peers. P2P users are usually interested in (a) retrieving data objects containing information of interest, like video and audio files, and (b) sharing information with other (participant) users or peers. From the information retrieval (IR) perspective, P2P users (a) typically submit short, loose queries by means of keywords derived from natural-language-style questions (e.g., “find all the music files containing Mozart’s compositions” is posed through the keywords compositions and Mozart), and (b), due to resource-sharing purposes, are usually interested in retrieving as a result a set of data objects rather than only one. Based on such set of items, well-founded IR methodologies like ranking can be successfully applied to improve system query capabilities, thus achieving performance better than that of more traditional database-like query schemes. Furthermore, the above-described P2P IR mechanism is self-alimenting as intermediate results can be then reused to share new information, or to set and specialize new search and query activities. In other words, from the database perspective, P2P users typically adopt a semistructured (data) model for querying data objects rather than a structured (data) model. On the other hand, efficiently accessing data in P2P systems, which is an aspect directly related to the above issues, is a relevant and still incompletely solved open research challenge.