ELITE: An Entailment-Based Federated Query Engine for Complete and Transparent Semantic Data Integration

In recent years the core of the semantic web has evolved to a conceptual layer built by a set of ontologies mapped onto data distributed in numerous data sources, interlinked, interpreted and processed in terms of its semantics. One of the central issues in this context became the federated querying of such linked data. This paper presents the federated query engine ELITE that facilitates a complete and transparent integration and querying of distributed autonomous data sources. To achieve this aim a combination of existing approaches for Ontologybased Data Access (OBDA) and federated query processing on Linked Open Data (LOD) are applied. Consolidating technologies like entailment regimes, the DL-Lite formalism, query rewriting, mapping relational data to RDF and an improved implementation of R-Tree based indexing contributes to the unique features of this federation engine. ELITE thereby enables the integration of various kinds of data sources, for example as relational databases or triple stores, simplicity of query design, guaranteed completeness of query results and highly efficient query processing. The federation engine has been developed and evaluated in the domain of carbon reduction in urban planning. Keywords—Federated Querying, Entailment Regime, Query Rewriting, Ontology-based Data Access (OBDA), DL-Lite, OWL QL, SPARQL, Linked Open Data (LOD), Indexing, R-Tree Index

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