We present a digital library architecture based on distributed hash tables. We discuss the main components of this architecture and the protocols for offering information retrieval and information filtering functionality. We present an experimental evaluation of our proposals.

We study the problem of offering publish/subscribe functionality on top of structured overlay networks using data models and languages from IR. We show how to achieve this by extending the distributed hash table Chord and present a detailed experimental evaluation of our proposals.

We study the problem of evaluating RDF queries over structured overlay networks.We consider the publish/subscribe scenario where nodes subscribewith long-standing queries and receive notifications whenever triples matching their queries are inserted in the network. In this paper we focus on conjunctive multi-predicate queries. We demonstrate that these queries are useful in various modern applications e.g., distributed digital libraries or Grid resource discovery. Conjunctive multipredicate queries are hard to answer since multiple triples are necessary for their evaluation, and these triples will usually be inserted in the network asynchronously. We present and evaluate query processing algorithms that are scalable and distribute the query processing load evenly.

This paper presents P2P-DIET, a resource sharing system that unifies ad-hoc and continuous query processing in super-peer networks using mobile agents. P2P-DIET offers a simple data model for the description of network resources based on attributes with values of type text. It also utilizes very efficient query processing algorithms based on indexing of resource metadata and queries. The capability of location-independent addressing is supported, which enables P2P-DIET clients to connect from anywhere in the network and use dynamic IP addresses. The features of stored notifications and rendezvous guarantee that all important information is delivered to interested clients even if they have been disconnected for some time. P2P-DIET has been developed on top of the Open Source mobile agent system DIET Agents and is currently been demonstrated as a file sharing application.

Publish/subscribe systems are an alternative to query based systems in cases where the same information is asked for over and over, and where clients want to get updated answers for the same query over a period of time. Recent publish/subscribe systems such as P2P-DIET have introduced this paradigm in the P2P context. In this paper we built on the experience gained with P2P-DIET and the Edutella P2P infrastructure and present the first implementation of a P2P publish/subscribe system supporting metadata and a query language based on RDF. We define formally the basic concepts of our system and present detailed protocols for its operation. Our work utilizes the latest ideas in query processing for RDF data, P2P indexing and routing research.

This paper presents P2P-DIET, an implemented resource sharing system that unifies one-time and continuous query processing in super-peer networks P2P-DIET offers a simple data model for the description of network resources based on attributes with values of type text and a query language based on concepts from Information Retrieval The focus of this paper is on the main modelling concepts of P2P-DIET (metadata, advertisements and queries), the routing algorithms (inspired by the publish/subscibe system SIENA) and the scalable indexing of resource metadata and queries.

We study the problem of selective dissemination of information in P2P networks. We present our work on data models and languages for textual information dissemination and discuss a related P2P architecture that motivates our efforts. We also survey our results on the computational complexity of three related algorithmic problems (query satisfiability, entailment and filtering) and present efficient algorithms for the most crucial of these problems (filtering). Finally, we discuss the features of P2P-DIET, a super-peer system we have implemented at the Technical University of Crete, that realizes our vision and is able to support both ad-hoc querying and selective information dissemination scenarios in a P2P framework.