Architecture of a p2p distributed adaptive directory

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Bookmarks are, nowadays, an important aid to navigation since they represent an easy way to reduce the cognitive load of managing and typing URLs. All the browsers have always provided, since the very beginning of the WWW, friendly ways of managing bookmarks. In this paper we deal with the problem of enriching this supportive framework for bookmarks (as provided by the browsers) by adding collaboration and (group) adaptation with a P2P system. In this paper, we describe a system that offers a distributed, cooperative and adaptive environment for bookmark sharing. DAD (Distributed Adaptive Directory) offers an adaptive environment since it provides suggestions about the navigation based on (a) the bookmarks, (b) the feedback implicitly provided by users and (c) the structure of the Web. DAD is fully scalable because of its peerto-peer architecture and provides, also, an infrastructure to build easily P2P overlay networks. Our system is structured on three separated layers (see Fig. 1): on the bottom we have an overlay network named CHILD (CHord with Identification and Lonely Discovery). Because of scalability and fault tolerance, our architecture is a pure Peer to Peer system: we realized a Distributed Hash Table (DHT) to store information about bookmarks. The DHT is based on the well-known Chord [5] protocol, which we extended with a boot mechanism through caching (i.e., no server is required), a mechanism that allows registration and authentication on the system and a tool that allows to save and reload the DHT data after the system shuts itself down or is started again. We would like to emphasize that the infrastructure provided by CHILD can be used as a base to develop a DHT for any pure P2P system. In fact, CHILD is implemented by a Java package that allows to build and manage any generic DHT, acting as middleware platform for P2P systems. The programmer can, therefore, implement the business logic of his application on top of our layer. CHILD will be soon freely available under the GNU public license at the project home page (http://isis.dia.unisa.it/projects/DAD).