Ontop is a Virtual Knowledge Graph (VKG) system. A VKG system exposes the content of arbitrary relational databases as knowledge graphs. These graphs are virtual, which means that data remains in the data sources instead of being moved to another database, and are realized through a conceptual representation of the domain of interest, provided in terms of an ontology, to which the data sources are mapped.
Ontop translates SPARQL queries expressed over the knowledge graphs into SQL queries executed by the relational data sources. It relies on R2RML mappings and OWL 2 QL ontologies.
Key features of Ontop are:
Ontop supports applications which want to get the advantage of the VKG technology in the following ways:
Ontop also comes in the form of a plugin for Protégé, providing a number of functionalities such as mappings bootstrapping and creation, or SPARQL query answering over the virtual knowledge graph.