Ontop
Ontop is a free, Apache 2.0-licensed Virtual Knowledge Graph system.
What Ontop is
Ontop is a free, Apache 2.0-licensed Virtual Knowledge Graph system. It exposes relational database content as virtual knowledge graphs while leaving data in source databases, then translates SPARQL queries into SQL executed by those sources. Ontop uses RDF 1.1, supports RDFS and OWL 2 QL ontologies, and accepts R2RML and Ontop mappings. It supports most SPARQL 1.1 features, including aggregation and GeoSPARQL functions. Documented databases include PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, DB2, Snowflake, Databricks, BigQuery, Redshift, DuckDB, DynamoDB, and TDengine. Federation integrations include Denodo, Dremio, Teiid, Spark, Trino, PrestoDB, and Athena. Deployment is available through a command-line SPARQL endpoint or Docker. Other tools provide virtual lenses, RDF-file materialization, and a Protégé mapping plugin. The plugin cannot handle lenses. Users must place a database JDBC driver in Ontop’s jdbc directory; generic JDBC may not support every setup or query.
Good
- Leaves data in source databases
- Translates SPARQL into SQL
- Supports RDF and OWL standards
- Offers Docker and CLI deployment
- Connects many database systems
Watch out
- JDBC drivers require manual installation
- Generic JDBC support is limited
- Protégé plugin lacks lens support
- Advanced use may need other editors
Who it suits
It suits teams that need ontology-based access to relational databases through SPARQL without moving source data. It is appropriate for users comfortable with mappings, JDBC drivers, and command-line or Docker deployment.
Verdict
Ontop provides standards-based virtual knowledge graphs across many relational systems and federators. Its mapping, JDBC, and plugin limitations make deployment details important for each database environment.
The facts
Each one read from Ontop's own pages, with the date it was checked.
What it does
- CLI capabilities
- The CLI includes commands for bootstrapping, starting an endpoint, extracting database metadata, materializing RDF, querying, validating and manipulating mappings.checked 8 Oct 2026
- Database driver requirement
- Users must manually download the JDBC driver for their database system and place it in Ontop's jdbc directory.checked 8 Oct 2026
- Database integrations
- Documented database systems include PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, DB2, Snowflake, Databricks, Google BigQuery, AWS Redshift, DuckDB, AWS DynamoDB, and TDengine.checked 8 Oct 2026
- Data handling
- The graphs are virtual, so data remains in its source databases rather than being moved to another database.checked 8 Oct 2026
- Deployment
- Ontop can be deployed as a SPARQL endpoint using its command-line interface or Docker image.checked 8 Oct 2026
- Downloads
- The project says its distributions are available through GitHub, Docker Hub, SourceForge, and the Protégé plugin repository.checked 8 Oct 2026
- Federation integrations
- Ontop supports database federators including Denodo, Dremio, Teiid, Apache Spark, Trino, PrestoDB, and AWS Athena.checked 8 Oct 2026
- Generic JDBC caveat
- Ontop warns that generic JDBC support is not sufficient for any data source and is not guaranteed to handle every database setup and SPARQL query correctly.checked 8 Oct 2026
- Generic JDBC limitation
- The generic JDBC implementation is not recommended because it may not handle every database setup and SPARQL query correctly; dialect-specific connectors are available for listed systems.checked 8 Oct 2026
- JDBC setup
- Users need to download the JDBC driver for their database system and place it in Ontop’s jdbc directory.checked 8 Oct 2026
- License
- Ontop is available under the Apache 2.0 license.checked 8 Oct 2026
- Materialization
- Ontop can materialize virtual graphs into RDF files.checked 8 Oct 2026
- Organizations
- The project says it is backed by the Free University of Bozen-Bolzano and Ontopic s.r.l., with regular contributions from Birkbeck, University of London, and Southeast University.checked 8 Oct 2026
- Other capabilities
- Ontop supports lenses as virtual views, can materialize virtual graphs into RDF files, and provides a Protégé plugin for editing and testing mappings.checked 8 Oct 2026
- Plugin limitation
- The Protégé plugin does not support lenses; the documentation recommends text editors or commercial offerings for advanced use.checked 8 Oct 2026
- Product
- Ontop is a Virtual Knowledge Graph system that exposes relational database content as knowledge graphs while leaving data in its source databases.checked 8 Oct 2026
- Project and license
- Ontop was initiated in 2009 by researchers at the Free University of Bozen-Bolzano and is available under the Apache 2.0 license.checked 8 Oct 2026
- Purpose
- Ontop exposes relational database contents as virtual knowledge graphs and translates SPARQL queries into SQL queries executed by the source databases.checked 8 Oct 2026
- Querying
- Ontop translates SPARQL queries over knowledge graphs into SQL queries executed by relational data sources.checked 8 Oct 2026
- SPARQL support
- It supports the majority of SPARQL 1.1 features, including main aggregation functions and GeoSPARQL functions.checked 8 Oct 2026
- Standards
- It uses RDF 1.1, supports RDFS and OWL 2 QL ontologies, and supports R2RML and Ontop mappings.checked 8 Oct 2026
- Support and commercial offerings
- The documentation says Ontopic provides a suite of solutions for leveraging Ontop and Virtual Knowledge Graphs; it does not state a support price or service level on that page.checked 8 Oct 2026
The company
- Headquarters
- Bolzano, Italychecked 28 Sep 2026
Where it runs
- Mapping editor
- A plugin for the Protégé ontology editor lets users edit and test mappings, but it does not support lenses.checked 8 Oct 2026
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