study a collection of heterogeneous XML databases maintain- ing similar and related information, exchanging data via a peer to peer overlay network. In this setting, a mediated global schema is unrealistic. Yet, users applications wish to query the d atabases via one peer using its schema. We have recently developed Hep- ToX, a P2P Heterogeneous XML database system. A key idea is that whenever a peer enters the system, it establishes an acquain- tance with a small number of peer databases, possibly with dif- ferent schema. The peer administrator provides correspondences between the local schema and the acquaintance schema using an informal and intuitive notation of arrows and boxes. We develop a novel algorithm that infers a set of precise mapping rules between the schemas from these visual annotations. We pin down a seman- tics of query translation given such mapping rules, and present a novel query translation algorithm for a simple but expressive frag- ment of XQuery, that employs the mapping rules in either direction. We show the translation algorithm is correct. Finally, we demon- strate the utility and scalability of our ideas and algorith ms with a detailed set of experiments on top of the Emulab, a large scale P2P network emulation testbed.
P2P systems with non-conventional lookups Popular P2P networks, e.g. Kazaa, Gnutella, advertise simple lookup queries on file names. The idea of building full-fledged P2P DBMS is being considered in many works. Internet-scale database queries and functionalities @cite_19 as well as approximate range queries in P2P @cite_18 and XPath queries in small communities of peers @cite_21 have been extensively dealt with. All these works do not deal with reconciling schema heterogeneity. @cite_21 relies on a DHT-based network to address simple XPath queries, while @cite_30 realizes IR-style queries in an efficient P2P relational database.
@cite_30 @cite_19 @cite_18 @cite_21
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We address the problem of querying XML data over a P2P network. In P2P networks, the allowed kinds of queries are usually exact-match queries over file names. We discuss the extensions needed to deal with XML data and XPath queries. A single peer can hold a whole document or a partial complete fragment of the latter. Each XML fragment document is identified by a distinct path expression, which is encoded in a distributed hash table. Our framework differs from content-based routing mechanisms, biased towards finding the most relevant peers holding the data. We perform fragments placement and enable fragments lookup by solely exploiting few path expressions stored on each peer. By taking advantage of quasi-zero replication of global catalogs, our system supports fast full and partial XPath querying. To this purpose, we have extended the Chord simulator and performed an experimental evaluation of our approach. In this paper, we address the problem of designing a scalable, accurate query processor for peer-to-peer filesharing and similar distributed keyword search systems. Using a globally-distributed monitoring infrastructure, we perform an extensive study of the Gnutella filesharing network, characterizing its topology, data and query workloads. We observe that Gnutella's query processing approach performs well for popular content, but quite poorly for rare items with few replicas. We then consider an alternate approach based on Distributed Hash Tables (DHTs). We describe our implementation of PIERSearch, a DHT-based system, and propose a hybrid system where Gnutella is used to locate popular items, and PIERSearch for handling rare items. We develop an analytical model of the two approaches, and use it in concert with our Gnutella traces to study the trade-off between query recall and system overhead of the hybrid system. We evaluate a variety of localized schemes for identifying items that are rare and worth handling via the DHT. Lastly, we show in a live deployment on fifty nodes on two continents that it nicely complements Gnutella in its ability to handle rare items. Peer-to-peer (P2P) systems show numerous advantages over centralized systems, such as load balancing, scalability, and fault tolerance, and they require certain functionality, such as search, repair, and message and data transfer. In particular, structured P2P networks perform an exact search in logarithmic time proportional to the number of peers. However, keyword similarity search in a structured P2P network remains a challenge. Similarity search for service discovery can significantly improve service management in a distributed environment. As services are often described informally in text form, keyword similarity search can find the required services or data items more reliably. This paper presents a fast similarity search algorithm for structured P2P systems. The new algorithm, called P2P fast similarity search (P2PFastSS), finds similar keys in any distributed hash table (DHT) using the edit distance metric, and is independent of the underlying P2P routing algorithm. Performance analysis shows that P2PFastSS carries out a similarity search in time proportional to the logarithm of the number of peers. Simulations on PlanetLab confirm these results and show that a similarity search with 34,000 peers performs in less than three seconds on average. Thus, P2PFastSS is suitable for similarity search in large-scale network infrastructures, such as service description matching in service discovery or searching for similar terms in P2P storage networks. Peer-to-peer systems enable access to data spread over an extremely large number of machines. Most P2P systems support only simple lookup queries. However, many new applications, such as P2P photo sharing and massively multi-player games, would benefit greatly from support for multidimensional range queries. We show how such queries may be supported in a P2P system by adapting traditional spatial-database technologies with novel P2P routing networks and load-balancing algorithms. We show how to adapt two popular spatial-database solutions - kd-trees and space-filling curves - and experimentally compare their effectiveness.