Access control is a recognized open issue when interacting with RDF using HTTP methods. In literature, authentication and authorization mechanisms either introduce undesired complexity such as SPARQL and ad-hoc policy languages, or rely on basic access control lists, thus resulting in limited policy expressiveness. In this paper we show how the Shi3ld attribute-based authorization framework for...

Query formulation is a key aspect of information retrieval, contributing to both the efficiency and usability of many semantic applications. A number of query languages, such as SPARQL, have been developed for the Semantic Web; however, there are, as yet, few tools to support end users with respect to the creation and editing of semantic queries. In this paper we introduce NITELIGHT, a Web-base...

We present QLever, a query engine for ecient combined search on a knowledge base and a text corpus, in which named entities from the knowledge base have been identi€ed (that is, recognized and disambiguated). Œe query language is SPARQL extended by two QLever-speci€c predicates ql:contains-entity and ql:contains-word, which can express the occurrence of an entity or word (the object of the pre...

The standard SPARQL query language is currently defined for querying RDF graphs without RDFS semantics. Several extensions to SPARQL have been proposed to query RDF graphs considering RDFS semantics. In this paper, we discuss extensions of SPARQL that uses regular expressions to navigate RDF graphs and may be used to answer queries considering RDFS semantics. In particular, we present and compa...

This paper reports on the participation of the system squall2sparql in the QALD-3 question answering challenge for DBpedia. squall2sparql is a translator from SQUALL, a controlled natural language for English, to SPARQL 1.1, a standard expressive query and update language for linked open data. It covers nearly all features of SPARQL 1.1, and is directly applicable to any SPARQL endpoint.

Linked data endpoints are online query gateways to semantically annotated linked data sources. In order to query these data sources, SPARQL query language is used as a standard. Although a linked data endpoint (i.e. SPARQL endpoint) is a basic Web service, it provides a platform for federated online querying and data linking methods. For linked data consumers, SPARQL endpoint availability and d...

Starting from the general framework for Annotated RDFS which we presented in previous work (extending Udrea et al’s Annotated RDF), we address the development of a query language – AnQL – that is inspired by SPARQL, including several features of SPARQL 1.1. As a side effect we propose formal definitions of the semantics of these features (subqueries, aggregates, assignment, solution modifiers) ...

The research on optimization of top-k SPARQL query would largely benefit from the establishment of a benchmark that allows comparing different approaches. For such a benchmark to be meaningful, at least two requirements should hold: 1) the benchmark should resemble reality as much as possible, and 2) it should stress the features of the topk SPARQL queries both from a syntactic and performance ...