Abstract
The database landscape has been significantly diversified during the last decade, resulting in the emergence of a variety of non-relational (also called NoSQL) databases, e.g., XML and JSON-document databases, key-value stores, and graph databases. To facilitate access to such databases and to enable data integration of non-relational data sources, we generalize the well-known ontology-based data access (OBDA) framework so as to allow for querying arbitrary databases through a mediating ontology. We instantiate this framework to MongoDB, a popular JSON-document database, and implement an prototype extension of the virtual OBDA system Ontop for answering SPARQL queries over MongoDB.