Ontop
Bolzano, Italy
What it is
Ontop is an open-source Virtual Knowledge Graph system that exposes relational database content as virtual knowledge graphs while data stays in its source databases. It translates SPARQL queries over those graphs into SQL executed by connected relational sources. Ontop uses RDF 1.1, supports RDFS and OWL 2 QL ontologies, and works with R2RML and Ontop mappings. It supports most SPARQL 1.1 features, including aggregation and GeoSPARQL functions. Documented database connections include PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, DB2, Snowflake, Databricks, Google BigQuery, AWS Redshift, DuckDB, AWS DynamoDB, and TDengine. Federation options include Denodo, Dremio, Teiid, Apache Spark, Trino, PrestoDB, and AWS Athena. It can run as a SPARQL endpoint through its CLI or Docker image, materialize graphs into RDF files, and provide virtual views called lenses. A Protégé plugin edits and tests mappings. Ontop is free under Apache 2.0 and supports Windows, macOS, Linux, web, API, and self-hosted deployments.
For and against
For
- Virtual graphs leave data in source databases
- Translates SPARQL queries into source SQL
- Supports many databases and federators
- CLI can query, validate, and materialize RDF
- Apache 2.0 open-source license
Against
- Protégé plugin does not support lenses
- JDBC drivers require manual installation
- Generic JDBC may not handle every setup
- No free trial is listed
The verdict
Ontop combines virtual knowledge graphs, SPARQL querying, and broad database connectivity without moving source data. Its mapping and JDBC requirements are important considerations for deployment planning.
Who it suits
Ontop suits teams that need ontology modeling, semantic reasoning, and SPARQL over relational databases. It is intended for users working with supported database systems, mappings, and RDF formats.
On the record
- CLI capabilities
- The CLI includes commands for bootstrapping, starting an endpoint, extracting database metadata, materializing RDF, querying, validating and manipulating mappings.ontop-vkg.org · read 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.ontop-vkg.org · read 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.ontop-vkg.org · read 8 Oct 2026
- Data handling
- The graphs are virtual, so data remains in its source databases rather than being moved to another database.ontop-vkg.org · read 8 Oct 2026
- Deployment
- Ontop can be deployed as a SPARQL endpoint using its command-line interface or Docker image.ontop-vkg.org · read 8 Oct 2026
- Downloads
- The project says its distributions are available through GitHub, Docker Hub, SourceForge, and the Protégé plugin repository.ontop-vkg.org · read 8 Oct 2026
- Federation integrations
- Ontop supports database federators including Denodo, Dremio, Teiid, Apache Spark, Trino, PrestoDB, and AWS Athena.ontop-vkg.org · read 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.ontop-vkg.org · read 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.ontop-vkg.org · read 8 Oct 2026
- JDBC setup
- Users need to download the JDBC driver for their database system and place it in Ontop’s jdbc directory.ontop-vkg.org · read 8 Oct 2026
- License
- Ontop is available under the Apache 2.0 license.ontop-vkg.org · read 8 Oct 2026
- Mapping editor
- A plugin for the Protégé ontology editor lets users edit and test mappings, but it does not support lenses.ontop-vkg.org · read 8 Oct 2026
- Materialization
- Ontop can materialize virtual graphs into RDF files.ontop-vkg.org · read 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.ontop-vkg.org · read 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.ontop-vkg.org · read 8 Oct 2026
- Plugin limitation
- The Protégé plugin does not support lenses; the documentation recommends text editors or commercial offerings for advanced use.ontop-vkg.org · read 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.ontop-vkg.org · read 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.ontop-vkg.org · read 8 Oct 2026
