Ontop: Answering SPARQL queries over relational databases

@article{Calvanese2017OntopAS,
  title={Ontop: Answering SPARQL queries over relational databases},
  author={Diego Calvanese and Benjamin Cogrel and Sarah Komla-Ebri and Roman Kontchakov and Davide Lanti and Mart{\'i}n Rezk and Mariano Rodriguez-Muro and Guohui Xiao},
  journal={Semantic Web},
  year={2017},
  volume={8},
  pages={471-487}
}
We present Ontop, an open-source Ontology-Based Data Access (OBDA) system that allows for querying relational data sources through a conceptual representation of the domain of interest, provided in terms of an ontology, to which the data sources are mapped. Key features of Ontop are its solid theoretical foundations, a virtual approach to OBDA, which avoids materializing triples and is implemented through the query rewriting technique, extensive optimizations exploiting all elements of the OBDA… 

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