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

# Apache Ossie

> Exchange semantic models with other tools using the Apache Ossie open specification

<Info>
  <Badge icon="test-pipe-2" color="orange" size="sm" shape="pill">Experimental</Badge> The Ossie integration is under active development and will be released soon, with the format interchange features it enables close behind. [What Experimental means](/support/feature-maturity-levels).
</Info>

[Apache Ossie (Incubating)](https://ossie.apache.org) — formerly the Open Semantic Interchange (OSI) — is an open, vendor-neutral specification for exchanging semantic models between tools. It defines a machine-readable format for describing datasets, relationships, fields, and metrics, along with the business context around them, so that any tool in a data stack can produce or consume semantic definitions without losing meaning.

The project is incubating at the Apache Software Foundation, developed in the open on GitHub, and backed by a coalition of data and analytics vendors. Its goal is to make a business concept like "Monthly Active Users" resolvable consistently across warehouses, BI tools, and AI agents, regardless of where it was originally defined.

## What Ossie covers

Ossie standardizes the shape of a semantic layer as an interchange format:

* **Semantic models** — the top-level unit exchanged between tools.
* **Datasets** — the queryable tables in a model.
* **Relationships** — how datasets connect to each other.
* **Fields** — the dimensions on each dataset.
* **Metrics** — the measures defined against fields.
* **AI context** — the descriptions and business meaning consumers (including AI agents) rely on.
* **Custom extensions** — a `custom_extensions` slot for tool-specific detail that would otherwise be lost in a round-trip.

## How Ossie maps to the Lightdash semantic layer

The [Lightdash semantic layer](/semantic-layer) already models the same building blocks Ossie standardizes:

| Ossie concept     | Lightdash equivalent                                                                  |
| ----------------- | ------------------------------------------------------------------------------------- |
| Semantic model    | A Lightdash project's models and their [YAML](/semantic-layer/yaml) / dbt definitions |
| Dataset           | A [table](/semantic-layer/tables)                                                     |
| Relationship      | [Joins](/semantic-layer/joins) between models                                         |
| Field (dimension) | [Dimensions](/semantic-layer/dimensions)                                              |
| Metric            | [Metrics](/semantic-layer/metrics)                                                    |

Lightdash will use Ossie as an interchange format for the semantic layer: you'll be able to import Ossie models into a Lightdash project, export a Lightdash project as Ossie, and round-trip through `custom_extensions` for detail the base spec does not yet cover.

## Where to learn more

* Apache Ossie project site: [ossie.apache.org](https://ossie.apache.org)
* Source and spec: [github.com/apache/ossie](https://github.com/apache/ossie)
* Lightdash semantic layer: [Lightdash semantic layer](/semantic-layer)