Suggestions appear as you type. Use the up and down arrows to choose one and Enter to open it.

This page's audience our own tag's counts — open to see them
–Visits
–Page views
–Clicks to vendors
–Time on page
–Reading now
Clicks to vendors, by tool
  • –
Top countries
  • –
Devices
  • –

– · visits, page views and clicks counted by our own tag, which counts more than our checked analytics; every figure rounded down · how we count

Ontop

Free#15 of 33 in Knowledge Graph SoftwareData Virtualization SoftwareQuery Engine Software

Ontop: An open-source layer for querying relational data as RDF knowledge graphs. Ranked #15 of 33 in Knowledge Graph Software by our editors (7.7/10); pricing: Open source; best for virtual knowledge graphs over relational databases.

7.7/10Editor score
Visit Ontop
Ontop7.7 Visit Ontop

At a glance

  • Editor score
    7.7 / 10
  • Pricing
    Open source
  • Best for
    Virtual knowledge graphs over relational databases
  • Paid from
    Free
  • Semantic reasoning
    Yes
  • Facts checked
    21 Sep 2026
Ontop screenshot

  • Where it wins

    • Translates SPARQL queries into SQL for existing relational sources
    • Supports RDFS, OWL 2 QL, R2RML, and native Ontop mappings
    • Connects with databases including PostgreSQL, Snowflake, and BigQuery

  • Where it doesn't

    • Requires relational databases and mapping work as its foundation
    • Its open-source model requires teams to manage deployment themselves
    • Its focus is semantic querying rather than a broad application suite

Our verdict on Ontop

Ontop is an open-source virtual knowledge graph system for teams that need to expose relational database content as RDF without moving the underlying data. It translates SPARQL queries over the virtual graph into SQL executed by relational data sources, making it suited to data integration, semantic querying, and knowledge graph deployments built on existing databases. Ontop supports RDFS and OWL 2 QL ontologies, SPARQL and predefined query endpoints, RDF graph materialization, and both R2RML and native Ontop mappings.

Its strongest fit is an environment with several relational or cloud data sources and a need for a shared semantic layer. The published integration list includes PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, DB2, Snowflake, Databricks, Google BigQuery, AWS Redshift, DuckDB, AWS DynamoDB, TDengine, Denodo, and Dremio. Database federation extends that reach, while virtual lenses let teams define views outside source databases. The Protégé plugin supports mapping design and testing, and Ontop can work across Windows, macOS, Linux, and API deployments.

Ontop is a focused technical choice rather than a hosted commercial service. Its open-source model suits teams that want control over deployment and a semantic interface over existing databases, but the approach depends on relational sources, ontology decisions, and mapping work. Teams choosing Ontop should be prepared to operate the software and shape how source schemas appear in RDF. It is a strong match for semantic querying and virtual knowledge graph projects; teams seeking a broader application suite should consider a different category of product.

Your product? Our editors can test Ontop in depth and publish a review, labelled as paid · from $149/mo →

Ontop pricing

Plans Open sourceFree Free to use — no paid tier required for the core job.
See plans on ontop-vkg.org

Ontop fact sheet

Free planNot verified
Paid fromFree
Ontology modelingYes
Semantic reasoningYes
RDF/SPARQL supportYes
Graph visualizationNot verified
Import formatsRDF/XML, Turtle, N-Triples, N-Quads, TriG, JSON-LD, R2RML, Ontop mapping format
DeploymentBoth
Query languagesSPARQL
DeploymentSelf-hosted
PlatformsWindows, macOS, Linux
SupportCommunity, Docs
Built forSmall business, Mid-market, Enterprise (editorial estimate)
Integrations20 integrations: PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, DB2 …
PricingOpen source
Websiteontop-vkg.org
Facts checked21 Sep 2026

Ontop integrations

Ontop lists 20 integrations on its own site.

  • PostgreSQL
  • MySQL
  • MariaDB
  • SQL Server
  • Oracle
  • DB2
  • Snowflake
  • Databricks
  • Google BigQuery
  • AWS Redshift
  • DuckDB
  • AWS DynamoDB
  • TDengine
  • Denodo
  • Dremio
  • Teiid
  • Apache Spark
  • Trino
  • PrestoDB
  • AWS Athena

Alternatives to Ontop

See all Ontop alternatives →

Also Ranked In

Ontop is ranked in 3 of our directories.

Used Ontop? Be the first to review it

The editor score above is our own research. What this page doesn't have yet is a reader's view — what you used Ontop for, what worked and what didn't. No stars are seeded and no review is paid for; an editor reads every one before it appears.

Write a reviewTwo minutes · verified accounts only · read by an editor before it appears

Reviews come only from verified accounts. Sign in or create an account first — your e-mail is never shown.

Your rating

0 characters · at least 80, up to 3,000

Posted from your verified account. Reviews appear after an editor reads them, usually within two working days.

Featured on iTechGuides

Featured on iTechGuides — Ontop 7.7/10

Ontop is listed in our Knowledge Graph Software directory. Add the badge to your site — it links back to this page.

<a href="https://www.itechguides.com/products/ontop-knowledge-graph-platform/"><img src="https://www.itechguides.com/best/badge/ontop-knowledge-graph-platform.svg" alt="Featured on iTechGuides" width="230" height="46"></a>

Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

Advertiser disclosure: iTechGuides is reader-supported. Vendors can pay for top positions in our rankings and for a place on other products' pages, and we may earn a commission when you click some links. Bought places stand at the number bought; this page and our disclosure say so. Paying vendors may get a fuller, more detailed review from our editors, and that review can change their score. How we rank.

Last updated · How we research and update