Ontop

A Virtual Knowledge Graph system that exposes relational databases as RDF knowledge graphs, translating SPARQL queries into SQL without moving data. Uses R2RML mappings and lightweight ontologies.

Visit website GitHub 938 stars

Overall rank: #18
First released: 2009
License: Apache-2.0
Built with: Java

Details

Vendor: Ontopic
Type: RDF
Kind: Query Engine
Category: Established
License: Apache-2.0
Language: Java
Query Languages: SPARQL
Protocols: SPARQL Protocol

Sources 5 references

Protocols SPARQL Protocol

Ontop only exposes a standard SPARQL 1.1 HTTP endpoint (e.g. /sparql); no separate generic REST management API was found, so HTTP/REST was dropped from the draft.

You can use POST or GET requests carrying the SPARQL query to evaluate (as per SPARQL HTTP protocol).
Interact with an Ontop SPARQL Endpoint | Ontop · reviewed 2026-08-02

Released 2009

Confirms the current value.

Ontop started in 2009, only one year after the first version of the SPARQL specification had been standardized
The Virtual Knowledge Graph System Ontop · reviewed 2026-08-02
Copyright (C) 2009 - 2025 Free University of Bozen-Bolzano
ontop/ontop · reviewed 2026-08-02

Language Java

Confirms the current value.

Currently, we use Maven 3.6+ and Java 11 to build the project.
ontop/ontop · reviewed 2026-08-02

License Apache-2.0

SPDX identifier as classified by GitHub from the repository licence file.

"spdx_id": "Apache-2.0"
GitHub licence API — ontop/ontop · reviewed 2026-08-02