Some Frequently Asked Questions

# General

# Which mapping syntaxes are supported?

We support R2RML (opens new window) and our own mapping syntax, which can be automatically converted into R2RML using Ontop CLI command ontop mapping to-r2rml

# Is it open source?

Yes! Ontop is available under the Apache License, Version 2.0.

# How can I report a bug or ask other questions?

You can get in touch with us through our support channels and contribute to the project by, for instance, filing a bug report.

# Does Ontop support SPARQL Update?

No, as for now, Ontop is a read-only system, it does not support SPARQL Update queries (opens new window) but only SELECT, CONSTRUCT, ASK and DESCRIBE queries. For more details, see the compliance page.

# How to set the log level to debug?

For both the Docker image and the CLI, set the environment variable ONTOP_LOG_LEVEL to debug.

# Protégé

# No suitable driver found for .. (driver)

You need to download and install the right JDBC driver in Protégé. This is required in order to query using SPARQL and use other features of Ontop. To add a new JDBC Driver:

  • in Protégé, go to Preference -> JDBC Drivers tab;
  • add a new entry;
  • type a description, e.g., PostgreSQL JDBC Driver;
  • type the driver’s class string, e.g., org.postgresql.Driver;
  • type or select the location of the driver’s JAR file, e.g., postgresql-8.4-701.jdbc4.jar;
  • click OK .

See also Setting up JDBC Drivers (opens new window) and JDBC Information (opens new window).

# No "JDBC drivers" tab in the preferences

You probably can see the following message in the Protégé console:

org.osgi.framework.BundleException: Activator start error in bundle org.protege.osgi.jdbc.prefs [20].)
org.protege.osgi.jdbc.RegistryException: java.lang.ClassNotFoundException: org.h2.Driver

Please go to the Preferences and click on "Reset preferences".

# Protégé does not show the Ontop tabs

To see the tabs go to Windows -> tabs -> Ontop Mappings and Ontop SPARQL.

# RDF4J workbench (not supported anymore)

# Why RDF4J Workbench refuses to delete some repositories?

For deleting metadata about a repository, the RDF4J Workbench should be able to create an instance of this repository. However, if the repository configuration is invalid (due to, for instance to bad mapping and ontology files), such an instance cannot be created. To avoid this situation, the configuration is validated in depth when a new repository is added to the Workbench. However, if the mapping and ontology files are changed afterwards, we offer no protection. One workaround is to create a valid repository with the same name and then to delete it. Another workaround is to delete it from the RDF4J console.