The RDF is a popular and well-documented format for publishing structured data on the web. It enables data to be consumed without the knowledge of how the data is internally stored. There are already ...several native RDF storage solutions that provide a SPARQL endpoint. However, native RDF stores are not widely adopted. It is still more common to store data in a relational database. One of the useful features of native RDF storage solutions is providing a SPARQL endpoint, a web service to query RDF data with SPARQL. To provide this feature also on top of prevalent relational databases, solutions for virtual SPARQL endpoints on top of a relational database have appeared. To benchmark these solutions, a state-of-the-art tool, the Berlin SPARQL Benchmark (BSBM), is used. However, BSBM was designed primarily to benchmark native RDF stores. It can also be used to benchmark solutions for virtual SPARQL endpoints. However, since BSBM was not designed for virtual SPARQL endpoints, each implementation uses that tool differently for evaluation. As a result, the evaluation is not consistent and therefore hardly comparable. In this paper, we demonstrate how this well-defined benchmarking tool for SPARQL endpoints can be used to evaluate virtual endpoints over relational databases, perform the evaluation on the available implementations, and provide instructions on how to repeat the same evaluation in the future.
Existing SPARQL-to-SQL translation techniques have limitations that reduce their robustness, efficiency and dependability. These limitations include the generation of inefficient or even incorrect ...SQL queries, lack of formal background, and poor implementations. Moreover, some of these techniques cannot be used over arbitrary DB schemas due to the lack of support for RDB to RDF mapping languages, such as R2RML. In this paper we present a technique (implemented in the -ontop- system) that tackles all these issues. We propose a formal approach for SPARQL-to-SQL translation that (i) generates efficient SQL by combining optimization techniques from the logic programming and SQL optimization fields; (ii) provides a well-defined specification of the SPARQL semantics used in the translation; and (iii) supports R2RML mappings over general relational schemas. We provide extensive benchmarks using the -ontop- system for Ontology Based Data Access (OBDA) and show that by using these techniques -ontop- is able to outperform well known SPARQL-to-SQL systems, as well as commercial triple stores, by several orders of magnitude.
Constitutional design and redesign is constant. Over the last 200 years, countries have replaced their constitutions an average of every 19 years and some have amended them almost yearly. A basic ...problem in the drafting of these documents is the search and analysis of model text deployed in other jurisdictions. Traditionally, this process has been ad hoc and the results suboptimal. As a result, drafters generally lack systematic information about the institutional options and choices available to them. In order to address this informational need, the investigators developed a web application, Constitute online at http://www.constituteproject.org, with the use of semantic technologies. Constitute provides searchable access to the world’s constitutions using the conceptualization, texts, and data developed by the Comparative Constitutions Project. An OWL ontology represents 330 “topics”–e.g. right to health–with which the investigators have tagged relevant provisions of nearly all constitutions in force as of September of 2013. The tagged texts were then converted to an RDF representation using R2RML mappings and Capsenta’s Ultrawrap. The portal implements semantic search features to allow constitutional drafters to read, search, and compare the world’s constitutions. The goal of the project is to improve the efficiency and systemization of constitutional design and, thus, to support the independence and self-reliance of constitutional drafters.
With the development of Internet technology, information management has shown a spurt of growth. In real-life applications, information usually includes spatial, temporal, or spatiotemporal features. ...Spatiotemporal data has temporal and spatial attributes, and these attributes are often fuzzy. Due to the great significance of fuzzy spatiotemporal data management, how to query fuzzy spatiotemporal data efficiently and effectively has become an important research issue. In that case, this paper formally proposes a new implementation method, which is the query processing of fuzzy spatiotemporal data. In view of the advantages of the most advanced mapping method (R2RML) in data transformation, three algorithms are proposed to transform fuzzy spatiotemporal data from relational database into fuzzy RDF data based on R2RML. On this basis, according to the characteristics of fuzzy RDF data, we give three different fuzzy quantifiers (extreme fuzzy quantifier, range fuzzy quantifier, degree fuzzy quantifier) to represent fuzzy spatiotemporal RDF data. Since SPARQL plays an important role in querying RDF data, it is used for the query of fuzzy spatiotemporal RDF data. In addition, three kinds of fuzzy quantifiers are designed, and the experimental results show the superiority of this method by analyzing experiments in the aspects of the recall and precision.
RDOTE – Publishing Relational Databases into the Semantic Web Vavliakis, Konstantinos N.; Grollios, Theofanis K.; Mitkas, Pericles A.
The Journal of systems and software,
January 2013, 2013-1-00, 20130101, Letnik:
86, Številka:
1
Journal Article
Recenzirano
► Quick and easy transformation of RDBMS into ontologies using a friendly GUI. ► Instantiate ontologies with real data for fast experimentation with large datasets. ► Import/export compatibility with ...D2RQ/R2RML mapping files. ► Definition of D2RQ/R2RML mappings with RDOTE's friendly interfaces.
A necessary step for the evolution of the traditional Web into a Semantic Web is the transformation of the vast quantities of data, currently residing in Relational Databases into semantically aware data. In addition, in cases where new ontology schemata are developed, considerable experimentation with real data for testing the consistency of classes, properties and entailment rules is required. During the last decade, there has been intense research and development in creating methodologies and tools able to map Relational Databases with the Resource Description Framework (RDF). Although some systems have gained wider acceptance in the Semantic Web community, they either require users to learn a declarative language for encoding mappings or, in case they support friendly user interfaces, they provide limited expressivity.
Thereupon, we present RDOTE, a framework for easily transporting data residing in Relational Databases into the Semantic Web. RDOTE is available under GNU/GPL license and it provides friendly graphical user interfaces, as well as enough expressivity for creating automatic and custom RDF dumps of relational data. RDOTE is also compatible with D2RQ and R2RML mapping definitions.
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