450 research outputs found
RDFViewS: A Storage Tuning Wizard for RDF Applications
In recent years, the significant growth of RDF data used in numerous
applications has made its efficient and scalable manipulation an important
issue. In this paper, we present RDFViewS, a system capable of choosing the
most suitable views to materialize, in order to minimize the query response
time for a specific SPARQL query workload, while taking into account the view
maintenance cost and storage space constraints. Our system employs practical
algorithms and heuristics to navigate through the search space of potential
view configurations, and exploits the possibly available semantic information -
expressed via an RDF Schema - to ensure the completeness of the query
evaluation
Principles of Experimental Evaluation
International audienceLa validation expérimentale est devenue incontournable pour faireaccepter les conclusions d'une étude scientifique, en particulier dansle domaine de la gestion de données. En même temps, mener à bien uneétude expérimentale complète et crédible demande de maîtriser unesérie de techniques et bonnes pratiques qui visent à organiser l'étudeexpérimentale, à analyser les résultats pour bien les interpréter, età rendre les expériences faciles à reproduire, afin de permettre à d'autres de les analyser et/ou de les refaire.Le tutoriel se concentre sur deux aspects liés à l'expérimentation, à savoir la planification des expériences, et les bonnes pratiques afinde rendre les expériences reproductibles. Une version étendue en a étéprésentée aux conférences ICDE 2008 et EDBT 2009
Query-Oriented Summarization of RDF Graphs
International audienceThe Resource Description Framework (RDF) is the W3C’s graph data model for Semantic Web applications. We study the problem of RDF graph summarization: given an input RDF graph G, find an RDF graph G' which summarizes G as accurately as possible, while being possibly orders of magnitude smaller than the original graph. Our approach is query-oriented, i.e., querying a summary of a graph should reflect whether the query has some answers against this graph. The summaries are aimed as a help for query formulation and optimization. We introduce two summaries: a baseline which is compact and simple and satisfies certain accuracy and representativeness properties, but may oversimplify the RDF graph, and a refined one which trades some of these properties for more accuracy in representing the structure
Teaching an RDBMS about ontological constraints
International audienceIn the presence of an ontology, query answers must reflect not only data explicitly present in the database, but also implicit data, which holds due to the ontology, even though it is not present in the database. A large and useful set of ontology languages enjoys FOL reducibility of query answering: answering a query can be reduced to evaluating a certain first-order logic (FOL) formula (obtained from the query and ontology) against only the explicit facts. We present a novel query optimization framework for ontology-based data access settings enjoying FOL reducibility. Our framework is based on searching within a set of alternative equivalent FOL queries, i.e., FOL reformulations, one with minimal evaluation cost when evaluated through a relational database system. We apply this framework to the DL-LiteR Description Logic underpinning the W3C's OWL2 QL ontology language, and demonstrate through experiments its performance benefits when two leading SQL systems, one open-source and one commercial, are used for evaluating the FOL query reformulations
Algebraic incremental maintenance of XML views
International audienceMaterialized views can bring important performance benefits when querying XML documents. In the presence of XML document changes, materialized views need to be updated to faithfully reflect the changed document. In this work, we present an algebraic approach for propagating source updates to XML materialized views expressed in a powerful XML tree pattern formalism. Our approach differs from the state of the art in the area in two important ways. First, it relies on set-oriented, algebraic operations, to be contrasted with node-based previous approaches. Second, it exploits state-of-the-art features of XML stores and XML query evaluation engines, notably XML structural identifiers and associated structural join algorithms. We present algorithms for determining how updates should be propagated to views, and highlight the benefits of our approach over existing algorithms through a series of experiments
XML content warehousing: Improving sociological studies of mailing lists and web data
In this paper, we present the guidelines for an XML-based approach for the
sociological study of Web data such as the analysis of mailing lists or
databases available online. The use of an XML warehouse is a flexible solution
for storing and processing this kind of data. We propose an implemented
solution and show possible applications with our case study of profiles of
experts involved in W3C standard-setting activity. We illustrate the
sociological use of semi-structured databases by presenting our XML Schema for
mailing-list warehousing. An XML Schema allows many adjunctions or crossings of
data sources, without modifying existing data sets, while allowing possible
structural evolution. We also show that the existence of hidden data implies
increased complexity for traditional SQL users. XML content warehousing allows
altogether exhaustive warehousing and recursive queries through contents, with
far less dependence on the initial storage. We finally present the possibility
of exporting the data stored in the warehouse to commonly-used advanced
software devoted to sociological analysis
The WebStand Project
In this paper we present the state of advancement of the French ANR WebStand
project. The objective of this project is to construct a customizable XML based
warehouse platform to acquire, transform, analyze, store, query and export data
from the web, in particular mailing lists, with the final intension of using
this data to perform sociological studies focused on social groups of World
Wide Web, with a specific emphasis on the temporal aspects of this data. We are
currently using this system to analyze the standardization process of the W3C,
through its social network of standard setters
Social, Structured and Semantic Search
International audienceSocial content such as blogs, tweets, news etc. is a rich source of interconnected information. We identify a set of requirements for the meaningful exploitation of such rich content, and present a new data model, called S3, which is the first to satisfy them. S3 captures social relationships between users, and between users and content, but also the structure present in rich social content, as well as its semantics. We provide the first top-k keyword search algorithm taking into account the social, structured, and semantic dimensions and formally establish its termination and correctness. Experiments on real social networks demonstrate the efficiency and qualitative advantage of our algorithm through the joint exploitation of the social, structured, and semantic dimensions of S3
RDF Analytics: Lenses over Semantic Graphs
International audienceThe development of Semantic Web (RDF) brings new requirements for data analytics tools and methods, going beyond querying to semantics-rich analytics through warehouse-style tools. In this work, we fully redesign, from the bottom up, core data analytics concepts and tools in the context of RDF data, leading to the first complete formal framework for warehouse-style RDF analytics. Notably, we define i) analytical schemas tailored to heterogeneous, semantics-rich RDF graph, ii) analytical queries which (beyond relational cubes) allow flexible querying of the data and the schema as well as powerful aggregation and iii) OLAP-style operations. Experiments on a fully-implemented platform demonstrate the practical interest of our approach
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