Resource Description Framework (RDF) is a language which represents information about resources. In order to search RDF resource descriptions, several RDF query languages such as RQL and SquishQL have been proposed. However, these RDF query languages do not use XML syntax and they have limited functionality. xRQL is proposed to solve these issues by defining an XML-based RDF query language with...

Recently, the use of the MapReduce framework for distributed RDF Schema reasoning has shown that it is possible to compute the deductive closure of sets of over a billion RDF triples within a reasonable time span [22], and that it is also possible to carry the approach over to OWL Horst [21]. Following this lead, in this paper we provide a MapReduce algorithm for the description logic EL+, more...

RDF Schema (RDFS) extends RDF with a schema vocabulary with a predefined semantics. Evaluating queries which involve this vocabulary is challenging, and there is not yet consensus in the Semantic Web community on how to define a query language for RDFS. In this paper, we introduce a language for querying RDFS data. This language is obtained by extending SPARQL with nested regular expressions th...

In this paper we benchmark three popular database representations of RDF/S schemata and data: (a) a schema-aware (i.e., one table per RDF/S class or property) with explicit (ISA) or implicit (NOISA) storage of subsumption relationships, (b) a schema-oblivious (i.e., a single table with triples of the form 〈subject-predicate-object〉), using (ID) or not (URI) identifiers to represent resources an...

SPARQL query containment under schema axioms is the problem of determining whether, for any RDF graph satisfying a given set of schema axioms, the answers to a query are contained in the answers of another query. This problem has major applications for verification and optimization of queries. In order to solve it, we rely on the μ-calculus. Firstly, we provide a mapping from RDF graphs into tr...

In this paper, we further develop a proposed layered approach for the Semantic Web. Our objective is to build a specific solution to the problem of providing data interoperability among different databases, so as to allow for schematic data integration. In particular, we solve the problem of translating queries on a database schema into queries on another database schema, using their relationsh...

The XML language and the object approach both aim at reusing and sharing their content through its improved structure. The XML galaxy is presented beginning with the XML basis (XML, namespaces, DTD and internal encoding), continuing with object-inspired structures (XMI, XML-Schema and Xquery) and modelling tools close to knowledge representation (RDF, RDF-Schema, Topic maps and OWL). Each langu...

Validata is an online web application for validating an RDF document against a set of constraints. This is useful for data exchange applications or ensuring conformance of an RDF dataset against a community agreed standard. Constraints are expressed as a Shape Expression (ShEx) schema. Validata extends the ShEx functionality to support multiple requirement levels. Validata can be repurposed for...

This is the fifth in a series of articles on ontology-based approaches to modeling. The main focus is on popular ontology languages proposed for the Semantic Web, such as the Resource Description Framework (RDF), RDF Schema (RDFS), and the Web Ontology Language (OWL). OWL is based on description logic. A later series of articles will explore other logic-based languages such as datalog. The firs...

With the explosion of the semantic web technologies, conventional SPARQL processing tools do not scale well for large amounts of RDF data because they are designed for use on a single-machine context. Several optimization solutions combined with cloud computing technologies have been proposed to overcome these drawbacks. However, these approaches only consider the SPARQL Basic Graph Pattern pro...