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

# Datasource Reference

> Use another existing datasource as a data source for a new datasource

<img src="https://mintcdn.com/reelevant/10tXeCE_biVlzX8s/images/datahub/source-datasource-v2.png?fit=max&auto=format&n=10tXeCE_biVlzX8s&q=85&s=d6c0d95cc8888283501811d8d13231f7" alt="Datasource reference configuration showing datasource picker" width="1280" height="800" data-path="images/datahub/source-datasource-v2.png" />

## Overview

The Datasource Reference source type lets you create a new datasource that reads data from another existing datasource. This is the foundation for derived datasources that compute or combine data from multiple sources.

## Configuration

| Field | Description                                                           |
| ----- | --------------------------------------------------------------------- |
| `id`  | The ID of an existing worker-mode datasource to use as a data source. |

<Info>
  Only **worker-mode** datasources (datasources that pull and store data) can be used as references. The referenced datasource must have a live version with data.
</Info>

## Use Cases

Datasource references are used in several special configurations:

| Configuration                    | Description                                                                                                                              |
| -------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
| **Merged Datasources**           | Combine two datasources by joining them on a common field. See [Special Configurations](/advanced-guide/datahub/special-configurations). |
| **Best Products**                | Compute top-performing products by combining a product catalog datasource with an analytics datasource.                                  |
| **Top Attributes**               | Identify preferred product attributes (brands, categories) per user based on behavioral data.                                            |
| **Bought Together (Cross-sell)** | Identify products frequently purchased together.                                                                                         |

## How It Works

1. The new datasource reads data from the referenced datasource's live storage instead of an external source.
2. Fields from the referenced datasource are available for [mapping](/advanced-guide/datahub/field-mapping) in the new datasource.
3. When the referenced datasource updates, the dependent datasource can automatically refresh (depending on the configured refresh schedule).

<Tip>
  You can chain datasource references to build multi-step data pipelines — for example, merge a product catalog with CRM data, then compute best products on the merged result.
</Tip>