# ontology

### Description

Use `ontology` to check if the instance in a case has a certain [role](https://docs.atfinity.io/guides/glossary/role). Based on that, you can require different [documents](https://docs.atfinity.io/guides/glossary/document). 

### Example

```
ah is AccountHolder
ah.ontology = Person
```

This expression checks if the instance in a case with the role AccountHolder is of the ontology Person.