Almer S. Tigelaar

Peer-to-Peer Information Retrieval: An Overview

Peer-to-peer technology is widely used for file sharing. In the past decade a number of prototype peer-to-peer information retrieval systems have been developed. Unfortunately, none of these has seen widespread real-world adoption and thus, in contrast with file sharing, information retrieval is still dominated by centralized solutions. In this article we provide an overview of the key challenges for peer-to-peer information retrieval and the work done so far. We want to stimulate and inspire further research to overcome these challenges. This will open the door to the development and large-scale deployment of real-world peer-to-peer information retrieval systems that rival existing centralized client-server solutions in terms of scalability, performance, user satisfaction, and freedom.

Automatic summarisation of discussion fora

Web-based discussion fora proliferate on the Internet. These fora consist of threads about specific matters. Existing forum search facilities provide an easy way for finding threads of interest. However, understanding the content of threads is not always trivial. This problem becomes more pressing as threads become longer. It frustrates users that are looking for specific information and also makes it more difficult to make valuable contributions to a discussion. We postulate that having a concise summary of a thread would greatly help forum users. But, how would we best create such summaries? In this paper, we present an automated method of summarising threads in discussion fora. Compared with summarisation of unstructured texts and spoken dialogues, the structural characteristics of threads give important advantages. We studied how to best exploit these characteristics. Messages in threads contain both explicit and implicit references to each other and are structured. Therefore, we term the threads hierarchical dialogues. Our proposed summarisation algorithm produces one summary of an hierarchical dialogue by ‘cherry-picking’ sentences out of the original messages that make up a thread. We try to select sentences usable for obtaining an overview of the discussion. Our method is built around a set of heuristics based on observations of real fora discussions. The data used for this research was in Dutch, but the developed method equally applies to other languages. We evaluated our approach using a prototype. Users judged our summariser as very useful, half of them indicating they would use it regularly or always when visiting fora.

Peer-to-peer information retrieval

The Internet has become an integral part of our daily lives. However,the essential task of finding information is dominated by a handful of large centralised search engines. In this thesis we study an alternative to this approach. Instead of using large data centres, we propose using the machines that we all use every day: our desktop, laptop and tablet computers, to build a peer-to-peer web search engine. We provide a definition of the associated research field: peer-to-peer information retrieval. We examine what separates it from related fields, give an overview of the work done so far and provide an economic perspective on peer-to-peer search. Furthermore, we introduce our own architecture for peer-to-peer search systems, inspired by BitTorrent. Distributing the task of providing search results for queries introduces the problem of query routing: a query needs to be sent to a peer that can provide relevant search results. We investigate how the content of peers can be represented so that queries can be directed to the best ones in terms of relevance. While cooperative peers can provide their own representation, the content of uncooperative peers can be accessed only through a search interface and thus they can not actively provide a description of themselves. We look into representing these uncooperative peers by probing their search interface to construct a representation. Finally, the capacity of the machines in peer-to-peer networks differs considerably, making it challenging to provide search results quickly. To address this, we present an approach where copies of search results for previous queries are retained at peers and used to serve future requests and show participation can be incentivised using reputations. There are still problems to be solved before a real-world peer-to-peer web search engine can be built. This thesis provides a starting point for this ambitious goal and also provides a solid basis for reasoning about peer-to-peer information retrieval systems in general.

Search result caching in peer-to-peer information retrieval networks

For peer-to-peer web search engines it is important to quickly process queries and return search results. How to keep the perceived latency low is an open challenge. In this paper we explore the solution potential of search result caching in large-scale peer-to-peer information retrieval networks by simulating such networks with increasing levels of realism. We find that a small bounded cache offers performance comparable to an unbounded cache. Furthermore, we explore partially centralised and fully distributed scenarios, and find that in the most realistic distributed case caching can reduce the query load by thirty-three percent. With optimisations this can be boosted to nearly seventy percent.