> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cognee.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Ontology

> Ground cognify extraction against an RDF/OWL, Turtle, or JSON-LD ontology so entities are matched to a known vocabulary.

## What it does

Supplies an ontology (RDF/OWL, Turtle, or JSON-LD) to cognify so extracted
entities are matched and grounded against a known vocabulary. The
[`OntologyResolver`](https://github.com/topoteretes/cognee-rs/blob/main/crates/ontology/src/) loads the file and matches
extracted entity names/types to ontology terms during knowledge-graph
extraction.

## When to use it

* You have a controlled vocabulary / taxonomy and want extraction to align with
  it (consistent entity types, canonical names).
* You want to constrain or normalize the messy free-form output of an LLM.

## CLI

`cognee-cli cognify` exposes the ontology file directly:

```bash theme={null}
cognee-cli cognify -d my_dataset --ontology-file ./ontologies/domain.owl
```

The flag is `--ontology-file <path>`
([`crates/cli/src/cli.rs`](https://github.com/topoteretes/cognee-rs/blob/main/crates/cli/src/cli.rs), `CognifyArgs`).

## Configuration (env / config keys)

You can also set the ontology globally instead of per-invocation:

| Env var                      | Config key                   | Default   |
| ---------------------------- | ---------------------------- | --------- |
| `ONTOLOGY_FILE_PATH`         | `ontology_file_path`         | *(empty)* |
| `ONTOLOGY_RESOLVER`          | `ontology_resolver`          | `rdflib`  |
| `ONTOLOGY_MATCHING_STRATEGY` | `ontology_matching_strategy` | `fuzzy`   |

```bash theme={null}
export ONTOLOGY_FILE_PATH=./ontologies/domain.owl
cognee-cli cognify -d my_dataset
```

Note: `ontology_resolver` and `ontology_matching_strategy` are stored for
parity but the active path currently uses the RDF/JSON-LD/Turtle resolver with a
fuzzy matching strategy whenever an ontology file is set. See
[Configuration](/rust/configuration) for the full surface and
[`crates/lib/src/config.rs`](https://github.com/topoteretes/cognee-rs/blob/main/crates/lib/src/config.rs) for the field
definitions and `set_ontology_*` setters.

## Supported formats

RDF/OWL, Turtle, and JSON-LD, parsed via the `sophia` family of crates. See
[`crates/ontology/`](https://github.com/topoteretes/cognee-rs/blob/main/crates/ontology/) for the resolver implementations and
the test fixtures under `crates/ontology/tests/fixtures/`.

## Pointers

* [`crates/ontology/`](https://github.com/topoteretes/cognee-rs/blob/main/crates/ontology/) — `OntologyResolver`, `RdfLibOntologyResolver`, `NoOpOntologyResolver`.
* [`crates/cli/src/cli.rs`](https://github.com/topoteretes/cognee-rs/blob/main/crates/cli/src/cli.rs) — `--ontology-file`.
* [Configuration](/rust/configuration) — ontology env vars.
* [Operations](/rust/operations) — cognify stage.