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

# Ontologies

> A catalog of source shapes

**Ontologies** is a schema catalog at [ontologies.aiql.io](https://ontologies.aiql.io). It describes the *shape* of connected data sources: classes, data properties, and object properties. It does not store the row-level data inside those sources.

The catalog holds source types such as databases and APIs. Pointing it at a source URL introspects that source and builds a schema instance others can reuse.

This product is distinct from Studio's in-workspace ontology and reference views. Studio applies ontologies inside a workspace so Observatory can reason. The catalog and introspection API is the [Ontologies API](/products/ontologies-api).