Top-K retrieval in peer to peer networks

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Categories and Subject Descriptors H.3.3 [Information Search and Retrieval]: Search Process; H.3.7 [Digital Libraries]: Collection General Terms Experimentation

The FacetedDBLP demonstrator allows to search compute

DL meets P2P - Distributed Document Retrieval based on Classification and Content

Peer-to-peer architectures are a potentially powerful paradigm for retrieving documents over networks of digital libraries avoiding single points of failure by massive federation of (independent) information sources. Today sharing files over P2P infrastructures is already immensely successful, but restricted to simple metadata matching. But when it comes to the retrieval of complex documents, capabilities as provided by digital libraries are needed. Digital libraries have to cope with compound documents. Though some document parts (like embedded images) can efficiently be retrieved using metadata matching, the text-based information needs different methods like full text search. However, for effective querying of texts, also information like inverted document frequencies are essential. But due to the distributed characteristics of P2P networks such 'collection-wide' information poses severe problems, e.g. that central updates whenever changes in any document collection occur use up valuable bandwidth

Caching for Improved Retrieval in Peer-to-Peer Networks

In modern information systems the dominant retrieval paradigms have shifted from exact matching towards retrieving a list of the most relevant objects

Progressive Distributed Top-k Retrieval in Peer-to-Peer Networks

Query processing in traditional information management systems has moved from an exact match model to more flexible paradigms allowing cooperative retrieval by aggregating the database objects' degree of match for each different query predicate and returning the best matching objects only. In peer-to-peer systems such strategies are even more important, given the potentially large number of peers, which may contribute to the results. Yet current peer-to-peer research has barely started to investigate such approaches. In this paper we will discuss the benefits of best match/top-k queries in the context of distributed peer-to-peer information infrastructures and show how to extend the limited query processing in current peer-to-peer networks by allowing the distributed processing of top-k queries, while maintaining a minimum of data traffic. Relying on a super-peer backbone organized in the HyperCuP topology we will show how to use local indexes for optimizing the necessary query routing and how to process intermediate results in inner network nodes at the earliest possible point in time cutting down the necessary data traffic within the network. Our algorithm is based on dynamically collected query statistics only, no continuous index update processes are necessary, allowing it to scale easily to large numbers of peers, as well as dynamic additions/deletions of peers. We will show our approach to always deliver correct result sets and to be optimal in terms of necessary object accesses and data traffic. Finally, we present simulation results for both static and dynamic network environments

Soft-X-ray fragmentation studies of molecular ions

International audienceImaging of photofragments from molecular ions after irradiation by soft X-ray photons has been realized at the ion beam infrastructure TIFF set up at the FLASH facility. Photodissociation of the two-electron system HeH + at 38.7 eV revealed the electronic excitations and the charge-state ratios for the products of this process, reflecting the non-adiabatic dissociation dynamics through multiple avoided crossings among the HeH + Rydberg potential curves. Dissociative ionization of the protonated water molecules H 3 O + and H 5 O + 2 at 90 eV revealed the main fragmentation pathways after the production of valence vacancies in these ionic species, which include a strong three-body channnel with a neutral fragment (OH + H + + H +) in H 3 O + photolysis and a significant two-body fragmentation channel (H 3 O + + H 2 O +) in H 5 O + 2 photolysis. The measurements yield absolute cross sections and fragment angular distributions. Increased precision and sensitivity of the technique was realized in recent developments, creating a tool for exploring X-ray excited molecular states under highly controlled target conditions challenging detailed theoretical understanding