# Reasoners

### Maintaining consistency via reasoning <a href="#evaluatingsnomedctconceptmodifications-maintainingconsistencyviareasoning" id="evaluatingsnomedctconceptmodifications-maintainingconsistencyviareasoning"></a>

There is a way to verify if the newly created components are semantically valid and if they maintain the consistency and coherence of the ontology. The reasoner classifies the ontology by computing the hierarchical relationships between the concepts which are based on their semantic definitions.

Snow Owl includes the following reasoner:

| Reasoner                                         | Description                                                                                                                                                                           |
| ------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [ELK](http://code.google.com/p/elk-reasoner/ELK) | An ontology reasoner with the goal of supporting the OWL 2 EL profile. Remains the world's fastest SNOMED CT classifier and is Snow Owl's default. ELK supports numerical data types. |

The reasoner set to default in the application preferences will be used for classification. In addition to the reasoners that are included with Snow Owl, it's also possible to install a different Protégé compatible reasoner. You can add a reasoner by copying the reasoner's Protégé jar to the dropins folder.

You can select the default reasoner in `File > Preferences > Snow Owl > Reasoners`.

New OWL API compliant reasoners can be added to Snow Owl in standalone mode by copying them into the dropins folder.

![Reasonsers Preferences Page](/files/ffdCX4U4cHfqtH5m7i2n)


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