Extending OAI-PMH over structured P2P networks for digital preservation

Open archives initiative (OAI) allows both libraries and museums create and share their own low-cost digital libraries (DL). OAI DL are based on OAI-PMH protocol which, although is consolidated as a pattern for disseminating metadata, does not rely on either digital preservation and availability of content, essential requirements in this type of system. Building new mechanisms that guarantee improvements, at no or low cost increases, becomes a great challenge. This article proposes a distributed archiving system based on a P2P network, that allows OAI-based libraries to replicate digital objects to ensure their reliability and availability. The proposed system keeps and extends the current OAI-PMH protocol characteristics and is designed as a set of OAI repositories, where each repository has an independent fail probability assigned to it. Items are inserted with a reliability that is satisfied by replicating them in subsets of repositories. Communication between the nodes (repositories) of the network is organized in a distributed hash table and multiple hash functions are used to select repositories that keep the replicas of each stored item. The OAI characteristics combined with a structured P2P digital preservation system allow the construction of a reliable and totally distributed digital library. The archiving system has been evaluated through experiments in a real environment and the OAI-PMH extension validated by the implementation of a proof-of-principle prototype.