Query Reformulation Algorithm Research Articles

View selection in Semantic Web databases

We consider the setting of a Semantic Web database, containing both explicit data encoded in RDF triples, and implicit data, implied by the RDF semantics. Based on a query workload, we address the problem of selecting a set of views to be materialized in the database, minimizing a combination of query processing, view storage, and view maintenance costs. Starting from an existing relational view selection method, we devise new algorithms for recommending view sets, and show that they scale significantly beyond the existing relational ones when adapted to the RDF context. To account for implicit triples in query answers, we propose a novel RDF query reformulation algorithm and an innovative way of incorporating it into view selection in order to avoid a combinatorial explosion in the complexity of the selection process. The interest of our techniques is demonstrated through a set of experiments.

OLAP query reformulation in peer-to-peer data warehousing

Inter-business collaborative contexts prefigure a distributed scenario where companies organize and coordinate themselves to develop common and shared opportunities, but traditional business intelligence systems do not provide support to this end. To fill this gap, in this paper we envision a peer-to-peer data warehousing architecture based on a network of heterogeneous peers, each exposing query answering functionalities aimed at sharing business information. To enhance the decision making process, an OLAP query expressed on a peer needs to be properly reformulated on the local multidimensional schemata of the other peers. To this end, we present a language for the definition of mappings between the multidimensional schemata of peers and we introduce a query reformulation framework that relies on the translation of mappings, queries, and multidimensional schemata onto the relational level. Then, we formalize a query reformulation algorithm and prove two properties: correctness and closure, that are essential in a peer-to-peer setting. Finally, we discuss the main implementation issues related to the reformulation setting proposed, with specific reference to the case in which the local multidimensional engines hosted by peers use the standard MDX language.

P2P schema‐mapping over network‐bound XML data

AbstractThe rise in availability of web‐based data sources has led to new challenges in data integration systems for obtaining decentralized, wide‐scale sharing of data preserving semantics. In this paper, we present a framework for integrating heterogeneous XML data sources distributed over a large‐scale, highly dynamic network of autonomous nodes. We highlight a query reformulation algorithm to combine and query‐distributed XML databases through a decentralized point‐to‐point mediation process among the different data sources by using P2P schema‐mappings. More precisely, our integration model is based on path‐to‐path mappings, using the XPath language. We demonstrate the usefulness and scalability of our ideas and algorithms with a detailed set of experiments. Finally, we discuss our experience implementing the above‐cited query reformulation algorithm as a Web service within the GDIS system, a service‐based Grid architecture. We have evaluated GDIS on several real‐world schemas with promising results. Copyright © 2010 John Wiley & Sons, Ltd.

Extended algorithm for XML query reformulation

Query reformulation is a key issue of the data integration,and it automatically rewrites the user's query request to the data source request directly.Recently the University of Michigan and the IBM AImaden Research Center presented a novel algorithm for constraint-based XML query reformulation,but it did not consider the problem of complex schema matching and limited the algorithm application.Based on the original query reformulation algorithm,an extended algorithm for XML query reformulation was presented,expanding the application scope of the original algorithm.The correctness and time complexity of the extended algorithm were also given.

A service-oriented system for distributed data querying and integration on Grids

Data Grids rely on the coordinated sharing of and interaction across multiple autonomous database management systems. They provide transparent access to heterogeneous and autonomous data resources stored on Grid nodes. Data sharing tools for Grids must include both distributed query processing and data integration functionality. This paper presents the implementation of a data sharing system that (i) is tailored to data Grids, (ii) supports well established and widely spread relational DBMSs, and (iii) adopts a hybrid architecture by relying on a peer model for query reformulation to retrieve semantically equivalent expressions, and on a wrapper-mediator integration model for accessing and querying distributed data sources. The system builds upon the infrastructure provided by the OGSA-DQP distributed query processor and the XMAP query reformulation algorithm. The paper discusses the implementation methodology, and presents empirical evaluation results.