GUN: An Efficient Execution Strategy for Querying the Web of Data

International audienceLocal-As-View (LAV) mediators provide a uniform interface to a federation of heterogeneous data sources, attempting to execute queries against the federation. LAV mediators rely on query rewriters to translate mediator queries into equivalent queries on the federated data sources. The query rewriting problem in LAV mediators has shown to be NP-complete, and there may be an exponential number of rewritings, making unfeasible the execution or even generation of all the rewritings for some queries. The complexity of this problem can be particularly impacted when queries and data sources are described using SPARQL conjunctive queries, for which millions of rewritings could be generated. We aim at providing an efficient solution to the problem of executing LAV SPARQL query rewritings while the gathered answer is as complete as possible. We formulate the Result-Maximal k-Execution problem (ReMakE) as the problem of maximizing the query results obtained from the execution of only k rewritings. Additionally, a novel query execution strategy called GUN is proposed to solve the ReMakE problem. Our experimental evaluation demonstrates that GUN outperforms traditional techniques in terms of answer completeness and execution time

Inferring user goals from sets of independent queries in a multidatabase environment

Loosely coupled data integration among networked sources has become so ubiquitous over the recent years that many of the services and applications used daily are actually not monolithic information systems but rather collections of sources tied together. Instead of building centralized and large data sources (i.e., the Extract- Transform-Load method), many organizations and individuals are opting for a virtual database approach. Especially along with the advent of service-oriented architectures, it has become very easy to leave data in its original source and to instead recruit the service provided by that source as needed. This structure is seen in a variety of scenarios such as hybrid web applications (mash-ups), enterprise information integration models, aggregation services and federated information retrieval systems. Furthermore, individual users are often forced to procure and assemble the information they need from sources distributed across a network. © 2010 Springer-Verlag Berlin Heidelberg

A query algebra for xml p2p databases

Abstract. One missing point in the current research about p2p XML databases is the definition of a proper query algebra that addresses p2pspecific issues, such as the dissemination and replication of data, the dynamic nature of the system, and the transient nature of data and replicas. This paper describes a query algebra for queries over XML p2p databases that provides explicit mechanisms for modeling data dissemination and replication constraints.

Some Algorithmic Improvments for the Containment Problem of Conjunctive Queries with Negation

International audienceQuery containment is a fundamental problem of databases. Given two queries q1 and q2, it asks whether the set of answers to q1 is included in the set of answers to q2 for any database. In this paper, we investigate this problem for conjunctive queries with negated subgoals. We use graph homomorphism as the core notion, which leads us to extend the results presented in [Ull97] and [WL03]. First, we exhibit sufficient (but not necessary) conditions for query containment based on special subgraphs of q2, which generalize that proposed in [WL03]. As a corollary, we obtain a case where the time complexity of the problem decreases. From a practical viewpoint, these properties can be exploited in algorithms, as shown in the paper. Second, we propose an algorithm based on the exploration of a space of graphs, which improves existing algorithms

Interview with Sueto Hayashida

The son of a plantation blacksmith recalls growing up in Japan and later in Keawe Camp. He describes his many household responsibilities and his plantation jobs, including delivery person, store order-taker, butcher, welder, and plumber.supervisor, delivery person, salesman, butcher, plumber; Japanese; maleInterview conducted in English.State, Privat