# Introduction

Ontop is a Virtual Knowledge Graph system. It 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.

Ontop translates SPARQL queries (opens new window) expressed over the knowledge graphs into SQL queries executed by the relational data sources. It relies on R2RML mappings (opens new window) and can take advantage of lightweight ontologies.

# Versions

This documentation is for Ontop 3.0 and more recent versions.

For earlier versions, please refer to our previous Wiki (opens new window).

Most recent version:

  • Stable: Ontop 4.1.0, released on February 28, 2021.

See release notes for more details.

# Main features

# Organizations

Ontop is backed by the Free University of Bozen-Bolzano (opens new window) and Ontopic s.r.l. (opens new window). It also receives regular important contributions from Birkbeck, University of London (opens new window). See the community section for more details.

# Licenses

Ontop is available under the Apache 2.0 (opens new window) license.

All the documentation is licensed under the Creative Commons (Attribution) (opens new window) license.

# Social

You can find us on the following social platforms:

# Citations