Catálogo de publicaciones - libros

In a broad sense, overlays can be setup as spaces “communities” for user, data or resource access, publishing and sharing, forming domains within a larger universe. Ad-hoc creation and linking of spaces can replace single linear address spaces or hierarchically structured ones. Our focus is on how can such completely independent and autonomous spaces be created and linked dynamically and information routed between them: we propose dynamic space management and inter-space linking and routing alternatives. We compare alternative gateway strategies and gateway hotspot avoidance. We also study the efficiency of the proposed schemes analytically.

Open peer-to-peer architectures offer many possibilities for replicating database content, but designers have to deal with problems such as peer churn rates and inherent uncertainty in decision making. The lack of global knowledge of peer characteristics poses the specific problem of reliable peer discovery for database replica placement. This paper describes a self-organising algorithm for generating a peer-to-peer gradient topology that helps to solve the problem of replica placement through the clustering of peers with similar uptime and performance characteristics. We evaluate the algorithm by simulation, and propose an approach for master-slave replication that exploits the properties of the presented topology.

In this paper we present a scalable and distributed access structure for similarity search in metric spaces. The approach is based on the Content–addressable Network (CAN) paradigm, which provides a Distributed Hash Table (DHT) abstraction over a Cartesian space. We have extended the CAN structure to support storage and retrieval of generic metric space objects. We use pivots for projecting objects of the metric space in an -dimensional vector space, and exploit the CAN organization for distributing the objects among the computing nodes of the structure. We obtain a Peer–to–Peer network, called the MCAN, which is able to search metric space objects by means of the similarity range queries. Experiments conducted on our prototype system confirm full scalability of the approach.

We study the problem of evaluating RDF queries over structured overlay networks. We consider the publish/subscribe scenario where nodes subscribe with 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 multi-predicate 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.

In this paper we propose a semantic based P2P system that incorporates peer , which allow a peer to state, for each of the concepts it deals with, the conditions under which it is available to process requests related to that concept. The semantic routing approach, based on advertisements and peer behavior in answering previous requests, takes also into account sharing policies.

In this paper, we present the use of semantic caching in the environment of schema-based super-peer networks. Different from traditional caching, semantic caching allows the answering of queries that are not in the cache directly. The challenge of answering the queries using the cache is reduced to the problem of answering queries using materialized views. For this purpose, we implemented the MiniCon-algorithm, which delivers the maximally-contained-rewritings of a posed query based on the stored views. Using simulation and experimental results, we will show the benefit of semantic caching.

We present a novel keyword search scheme for file sharing applications based on (CDA). Through CDA, we are able to associate node IDs with content distances and thus reduce several complex keyword queries to routing problems on structured overlays. Unlike traditional approaches, we require neither set intersection process nor replication for query processing as a result of content distance addressing. In this paper, we present the design and theoretical analysis of CDA for keyword search as well as simulation results using real world parameters.

This paper addresses the problem of data placement, indexing, and querying large XML data repositories distributed over an existing P2P service infrastructure. Our architecture scales gracefully to the network and data sizes, is fully distributed, fault tolerant and self-organizing, and handles complex queries efficiently, even those queries that use full-text search. Our framework for indexing distributed XML data is based on both meta-data information and textual content. We introduce a novel data synopsis structure to summarize text that correlates textual with positional information and increases query routing precision. Our processing framework maps an XML query with full-text search into a distributed program that migrates from peer to peer, collecting relevant document locations along the way. In addition, we introduce methods to handle network updates, such as node arrivals, departures, and failures. Finally, we report on a prototype implementation, which is used to validate the accuracy of our data synopses and to analyze the various costs involved in indexing XML data and answering queries.

The both-as-view (BAV) approach to data integration has the advantage of specifying mappings between schemas in a bidirectional manner, so that once a BAV mapping has been established between two schemas, queries may be exchanged in either direction between the schemas. In this paper we discuss the reformulation of queries over BAV transformation pathways, and demonstrate the use of this reformulation in two modes of query processing. In the first mode, public schemas are shared between peers and queries posed on the public schema can be reformulated into queries over any data sources that have been mapped to the public schema. In the second, queries are posed on the schema of a data source, and are reformulated into queries on another data source via any public schema to which both data sources have been mapped.

This paper presents a scalable and robust IPv4/IPv6 transition method utilizing Peer-to-peer technology. The gateways of IPvX (IPv4 or IPv6) islands automatically set up an IPvX P2P network upon IPvY (IPv6 or IPv4) network to exchange and maintain IPv4/IPv6 transition information. IPvX in IPvY tunnels between IPvX islands can be established automatically according to the IPv4/IPv6 transition information.