Summary Prefix Tree: An over DHT Indexing Data Structure for Efficient Superset Search

International audienceThis paper presents the summary prefix tree (SPT), a trie data structure that supports efficient superset searches over DHT. Each document is summarized by a Bloom filter which is then used by SPT to index this document. SPT implements an hybrid lookup procedure that is well-adapted to sparse indexing keys such as Bloom filters. It also proposes a mapping function that permits to mitigate the impact of the skewness of SPT due to the sparsity of Bloom filters, especially when they contain only few words. To perform efficient superset searches, SPT maintains on each node a local view of the global tree. The main contributions are the following. First, the approximation of the superset relationship among keyword-sets by the descendance relationship among Bloom filters. Second, the use of a summary prefix tree (SPT), a trie indexing data structure, for keyword-based search over DHT. Third, an hybrid lookup procedure which exploits the sparsity of Bloom filters to offer good performances. Finally, an algorithm that exploits SPT to efficiently find descriptions that are supersets of query keywords

Optimizando los indices invertidos para la búsqueda de palabras en sistemas P2P

La búsqueda de objetos a través de palabras es una componente crítica en un sistema P2P. Este no es un tema trivial en las redes estructuradas como las DHTs, dado que solo permiten búsqueda de palabras exactas. Se han propuesto diversas soluciones a este problema, pero es difícil encontrar una eficiente. Los índices invertidos son una solución sencilla, intuitiva, donde encontrar los resultados es directo, pero en su forma más simple presentan varias falencias, como carga desbalanceada, hot spots, pobre tolerancia a fallas y no permitir la búsqueda de palabras inexactas. En este paper presentamos una solución utilizando índices invertidos, donde se contemplan los problemas planteados y se resuelven con diversas técnicas, obteniéndose un sistema robusto y eficiente, que cumple con los requisitos de un motor de búsqueda para sistemas peer-to-peer.Workshop de Procesamiento Distribuido y Paralelo (WPDP)Red de Universidades con Carreras en Informática (RedUNCI

Optimizando los indices invertidos para la búsqueda de palabras en sistemas P2P

La búsqueda de objetos a través de palabras es una componente crítica en un sistema P2P. Este no es un tema trivial en las redes estructuradas como las DHTs, dado que solo permiten búsqueda de palabras exactas. Se han propuesto diversas soluciones a este problema, pero es difícil encontrar una eficiente. Los índices invertidos son una solución sencilla, intuitiva, donde encontrar los resultados es directo, pero en su forma más simple presentan varias falencias, como carga desbalanceada, hot spots, pobre tolerancia a fallas y no permitir la búsqueda de palabras inexactas. En este paper presentamos una solución utilizando índices invertidos, donde se contemplan los problemas planteados y se resuelven con diversas técnicas, obteniéndose un sistema robusto y eficiente, que cumple con los requisitos de un motor de búsqueda para sistemas peer-to-peer.Workshop de Procesamiento Distribuido y Paralelo (WPDP)Red de Universidades con Carreras en Informática (RedUNCI

SPT – Summary Prefix Tree: An over DHT Indexing Data Structure for Efficient Superset Search

This paper presents the summary prefix tree (SPT), a trie data structure that supports efficient superset searches over DHT. Each document is summarized by a Bloom filter which is then used by SPT to index this document. SPT implements an hybrid lookup procedure that is well-adapted to sparse indexing keys such as Bloom filters. We also propose a mapping function that permits to mitigate the impact of the skewness of SPT due to the sparsity of Bloom filters, especially when they contain only few words. To perform superset searches, SPT maintains on each node a local view of the global tree. The main contributions are the following. First, the approximation of the superset relationship among keyword-sets by the descendant relationship among Bloom filters. Second, the use of a summary prefix tree, a trie indexing data structure, for keyword-based search over DHT. Third, a hybrid lookup procedure which exploits the sparsity of Bloom filters to offer good performances. Finally, an algorithm that exploits SPT to efficiently find descriptions that are supersets of query keywords.Cet article présente un arbre de préfixes SPT, une structure de données qui permet de réaliser efficacement des recherches de sur-ensemble sur DHT. Chaque document est résumé par un filtre Bloom qui est ensuite utilisé par SPT pour indexer ce document. SPT implémente une procédure de recherche hybride qui est bien adaptée aux clés d'indexation éparses telles que les filtres Bloom. Nous proposons aussi une fonction de mapping qui atténue l'impact de l'asymétrie de SPT en raison de la rareté des bit 1 dans les filtres de Bloom, surtout lorsqu'ils ne contiennent que peu de mots. Pour effectuer des recherches de sur-ensemble, SPT maintient sur chaque noeud une vue locale de l'arbre global. Les principales contributions sont les suivantes. Premièrement, l'approximation de la relation de sur-ensemble entre les ensembles de mots-clés par la relation descendance entre les filtres Bloom. Deuxièmement, l'utilisation d'un arbre de préfixes (SPT), une structure d'indexation de données pour la recherche par mot-clé sur DHT. Troisièmement, une procédure de recherche hybride qui exploite la nature éparse des filtres Bloom pour offrir de bonnes performances. Enfin, un algorithme qui exploite SPT pour trouver efficacement des descriptions qui sont des sur-ensembles d'une requête de mots-clés

Ricerca per parole chiave basata su DHT

Questo lavoro di tesi mira a fornire una panoramica sulle tecnologie utilizzate nella classe dei sistemi distribuiti, con considerevole enfasi sulle DHT (Distributed Hash Table). In particolare, verranno descritti i vantaggi che queste reti offrono rispetto ai tradizionali approcci. Fondamentale sarà sottolineare come le operazioni di memorizzazione, di ricerca e di recupero delle informazioni siano più efficaci da eseguire su sistemi P2P, in quanto permetto il funzionamento corretto delle applicazioni che ne fanno uso. Sarà presentato un famoso protocollo di DHT, Chord. Questo protocollo si differenzia dai servizi tradizionali, in quanto fornisce una scalabilità migliore, ha un tipo di memorizzazione più semplice e presenta una routing table senza incoerenze che viene detta stabile. Verranno, tuttavia, descritti alcuni dubbi che riguarderanno la ricerca per parole chiave. Pertanto, si analizzerà un sistema preso come riferimento tra le soluzioni a tale problema. Verrà quindi descritta una struttura ad ipercubo a r-dimensioni, con una stringa composta da r-bit. Verrà approfondita applicandola poi ad una struttura applicata a una tabella hash distribuita. Il focus principale della tesi, una volta data l’infarinatura generale dei vari concetti, è quello di analizzare una particolare tecnica di ricerca di oggetti all’interno di reti P2P che evitano problemi di un- balanced load, hot spots, fault tolerance, storage redundancy, e unable to facilitate ranking. La struttura logica che seguirà è la seguente: Il capitolo 1, dando uno sguardo alle Distributed Hash Table, si focalizzerà sul protocollo Chord. Nel capitolo 2 verrà il problema delle keyword search in reti p2p. Il capitolo 3 seguirà la struttura del capitolo due, rappresentando le soluzioni proposte attraverso l’utilizzo di simulazioni atte a rappresentarne i vantaggi. Il capitolo 4 sarà dedicato ad alcune considerazioni conclusive

Complex queries over decentralised systems for geodata retrieval

none4sìDecentralised systems have been proved to be quite effective to allow for trusted and accountable data sharing, without the need to resort to a centralised party that collects all the information. While complete decentralisation provides important advantages in terms of data sovereignty, absence of bottlenecks and reliability, it also adds some issues concerned with efficient data lookup and the possibility to implement complex queries without reintroducing centralised components. In this paper, we describe a system that copes with these issues, thanks to a multi-layer lookup scheme based on Distributed Hash Tables that allows for multiple keyword-based searches. The service of peer nodes participating in this discovery service is controlled and rewarded for their contribution. Moreover, the governance of this process is completely automated through the use of smart contracts, thus building a Decentralised Autonomous Organization (DAO). Finally, we present a use case where road hazards are collected in order to test the goodness of our system for geodata retrieval. Then, we show results from a performance evaluation that confirm the viability of the proposal. © 2022 The Authors. IET Networks published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology. openZichichi, Mirko; Serena, Luca; Ferretti, Stefano; D'Angelo, GabrieleZichichi, Mirko; Serena, Luca; Ferretti, Stefano; D'Angelo, Gabriel

A Novel Locality Algorithm and Peer-to-Peer Communication Infrastructure for Optimizing Network Performance in Smart Microgrids

[EN] Peer-to-Peer (P2P) overlay communications networks have emerged as a new paradigm for implementing distributed services in microgrids due to their potential benefits: they are robust, scalable, fault-tolerant, and they can route messages even with a large number of nodes which are frequently entering or leaving from the network. However, current P2P systems have been mainly developed for file sharing or cycle sharing applications where the processes of searching and managing resources are not optimized. Locality algorithms have gained a lot of attention due to their potential to provide an optimized path to groups with similar interests for routing messages in order to get better network performance. This paper develops a fully functional decentralized communication architecture with a new P2P locality algorithm and a specific protocol for monitoring and control of microgrids. Experimental results show that the proposed locality algorithm reduces the number of lookup messages and the lookup delay time. Moreover, the proposed communication architecture heavily depends of the lookup used algorithm as well as the placement of the communication layers within the architecture. Experimental results will show that the proposed techniques meet the network requirements of smart microgrids even with a large number of nodes on stream.This work is supported by the Spanish Ministry of Economy and Competitiveness (MINECO) and the European Regional Development Fund (ERDF) under Grant ENE2015-64087-C2-2R. This work is supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under BES-2013-064539.Marzal-Romeu, S.; González-Medina, R.; Salas-Puente, RA.; Figueres Amorós, E.; Garcerá, G. (2017). A Novel Locality Algorithm and Peer-to-Peer Communication Infrastructure for Optimizing Network Performance in Smart Microgrids. 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Decentralized Personal Data Marketplaces: How Participation in a DAO Can Support the Production of Citizen-Generated Data

Big Tech companies operating in a data-driven economy offer services that rely on their users’ personal data and usually store this personal information in “data silos” that prevent transparency about their use and opportunities for data sharing for public interest. In this paper, we present a solution that promotes the development of decentralized personal data marketplaces, exploiting the use of Distributed Ledger Technologies (DLTs), Decentralized File Storages (DFS) and smart contracts for storing personal data and managing access control in a decentralized way. Moreover, we focus on the issue of a lack of efficient decentralized mechanisms in DLTs and DFSs for querying a certain type of data. For this reason, we propose the use of a hypercube-structured Distributed Hash Table (DHT) on top of DLTs, organized for efficient processing of multiple keyword-based queries on the ledger data. We test our approach with the implementation of a use case regarding the creation of citizen-generated data based on direct participation and the involvement of a Decentralized Autonomous Organization (DAO). The performance evaluation demonstrates the viability of our approach for decentralized data searches, distributed authorization mechanisms and smart contract exploitation

Gestione e Indicizzazione di Dati in Contesti di Smart Transportation: un Approccio basato su Registri Distribuiti

Veicoli a guida autonoma, nuovi modelli di Smart Mobility e servizi sempre più personalizzati stanno trasformando il mondo automobilistico che esige sempre più in sicurezza e affidabilità. I sistemi di trasporto intelligenti (ITS) consentono di affrontare in modo innovativo i problemi legati alla mobilità, attraverso soluzioni improntate su sicurezza, efficienza, efficacia e rispetto per l’ambiente. La loro realizzazione, però, comporta il superamento di alcuni aspetti che devono essere considerati e che sono legati alla raccolta, alla memorizzazione e al livello di affidabilità dei dati. Lo scopo del presente lavoro è quello di presentare un sistema di crowdsourcing decentralizzato, ideato per il contesto di Smart Transportation, che fa uso di un robusto schema di indicizzazione dei dati, pensato come alternativa ai tipici schemi centralizzati, sempre più frequentemente oggetto di attacchi e uso improprio. Interamente basato su tecnologie distribuite, oltre a fornire tracciabilità e immutabilità dei dati, il sistema in questione fa uso di una Distributed Hash Table come livello posto sopra la DLT, al fine di migliorare la gestione dei dati in un contesto in cui l'attenzione degli utenti è in progressivo incremento e dove, inoltre, efficacia e efficienza si rivelano più che importanti, necessari