RDF-based Peer-to-Peer-Networks for Distributed (Learning) Repositories

Metadata for the World Wide Web are important, but metadata for Peer-to-Peer (P2P) networks are absolutely crucial. In this paper we discuss the open source project Edutella, which combines semantic web and peer-to-peer technologies in order to make distributed learning repositories possible and useful. We describe the main services of the Edutella network infrastructure and its architecture based on the exchange of RDF metadata, and specify the query service (based on the Edutella Common Data Model and Query Exchange Language RDFQEL) as one of the core services of Edutella. As a schema-based peer-to-peer network, Edutella extends conventional peer-to-peer networks by allowing different and extensible schemas to describe peer content, a necessary feature for information rich peer-to-peer networks. We describe and discuss the HyperCuP topology, which implements an optimal broadcast topology, and show how it can be used to form the backbone of a super-peer-based topology suitable for schema-based peer-to-peer networks, including appropriate routing indices for super-peer/superpeer connections as well as for super-peer/peer connections. We also discuss an extension of this architecture providing additional capabilities for inferences and model transformation based on the TRIPLE language. Finally, we discuss the use of the Edutella infrastructure in the EU/IST ELENA project which aims to create smart spaces for learning.