# is

**Existence declarations** are the simplest declarations you can create. Each of these declarations must be fulfilled for the document or rule to match. However, for each possible combination multiple matches are created.

### Syntax

`VARIABLE is ONTOLOGY, ROLE_1, ..., ROLE_N`

A match with the name `VARIABLE` is created for an Instance that has the Ontology `ONTOLOGY` and all the roles (`ROLE_1` to `ROLE_N`) mentioned.

A declaration is also valid if there is either an Ontology or a list of Roles after the `is`; providing both of them is optional.

### Example: Just an Ontology

```python
p is Person
```

If there is a `Person` Instance in the Case, it will be available in the variable `p`.

### Example: Just a Role

```python
p is AccountHolder
```

If there is an Ontology Instance with the role `AccountHolder` in the *Case*, it will be available in the variable `p`.

### Example: Ontology and Role

```python
p is Person, AccountHolder
```

If there is a `Person` Instance that has the Role `AccountHolder` in the Case, it will be available in the variable `p`.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.atfinity.io/rule-language/declarations/is-ontology-role.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.