Data and Knowledge Group

― Knowledge Representation and Reasoning

HermiT OWL Reasoner

The New Kid on the OWL Block


HermiT is reasoner for ontologies written using the Web Ontology Language (OWL). Given an OWL file, HermiT can determine whether or not the ontology is consistent, identify subsumption relationships between classes, and much more.

HermiT is the first publicly-available OWL reasoner based on a novel “hypertableau” calculus which provides much more efficient reasoning than any previously-known algorithm. Ontologies which previously required minutes or hours to classify can often by classified in seconds by HermiT, and HermiT is the first reasoner able to classify a number of ontologies which had previously proven too complex for any available system to handle.

HermiT uses direct semantics and passes all OWL 2 conformance tests for direct semantics reasoners.

We have now released HermiT 1.3.8 under the GNU Lesser General Public License (LGPL). The release should be compatible with Java 1.5 or higher. HermiT 1.3.8 uses the OWL API 3.4.3, which is backwards compatible with the OWL API 3.3.x, 3.2.x and 3.1.x, but not backwards compatible with the OWL API 3.0.x.

Since version 1.1, HermiT can handle DL Safe rules and the rules can directly be added to the input ontology in functional style or other OWL syntaxes supported by the OWL API (see A Syntax for Rules in OWL 2). Note that reasoning with DL Safe rules is incomplete if the ontology contains property chains or transitivity axioms and complex properties are used in the rule bodies.

HermiT is open-source and released under LGPL. All components and source code is included in the project folder of the release.


Using HermiT

HermiT as Protégé plug-in

Protégé 4.3 release is now available and it comes with HermiT pre-installed. Alternatively, the file org.semanticweb.HermiT.jar from the latest HermiT release can be copied into Protege's plugin folder. Note that Protégé 4.1 beta (and more recent versions) work with HermiT 1.3.x, whereas Protégé 4.1 alpha works only with the OWL API 3.0.0 and HermiT 1.2.x.

HermiT from the command line

HermiT provides a command-line interface for common reasoning tasks, including classification and query answering.

HermiT in Java applications

HermiT supports the OWLReasoner interface from the OWL API and has native support for working with objects such as ontologies and class expression from the OWL API.


HermiT 1.3.8 is now available

Version 1.3.8 uses OWL API 3.4.3, and has some bug fixes as described in the readme.

HermiT nightly builds available

We now provide nightly builds of HermiT. These are experimental and not guaranteed to work, but for users who eagerly await some new feature or bug-fix, it can be worth trying. JUnit test reports are now available and unless we are in the middle of major changes, HermiT should always pass all tests.