# Occurrence Types

> The different types of occurrences in Asset Transformer Studio

Depending on the components it carries, an occurrence is designated by a different name in Asset Transformer Studio's user interface, API and documentation:

| Occurrence type         | Description                                                                                                                                                                                                                                                                                                                                                                                                                                              | Common Name      | Icon                                                                                                              |
| ----------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------- | ----------------------------------------------------------------------------------------------------------------- |
| **Part occurrence**     | An occurrence with a [Part component](./occurrence-components.md#part-component) is a `Part occurrence`, more commonly called `Part`. For example, the function `Merge Parts` merges together several Part occurrences in one resulting Part occurrence, and combines their geometries in its `Part component`.                                                                                                                                          | Part             | ![Part icon](/api/media?file=/asset-transformer-studio/2026.5.0/media/STUDIO_PS-Icons_PartOccurrence.jpg)         |
| **Assembly occurrence** | An occurrence with no [Part component](./occurrence-components.md#part-component), and having other occurrences as children, is called an `Assembly occurrence`, or `Assembly`. An Assembly is basically a node used to store other nodes, like a group or a folder. For example, the function **Merge Parts By Assemblies** finds all the Assembly occurrences in the Tree and merges their Part occurrences children as one resulting Part occurrence. | Assembly         | ![Assembly icon](/api/media?file=/asset-transformer-studio/2026.5.0/media/STUDIO_PS-Icons_AssemblyOccurrence.jpg) |
| **Empty occurrence**    | An occurrence containing no geometry (no [Part component](./occurrence-components.md#part-component) or a [Part component](./occurrence-components.md#part-component) containing no geometry), no light (no [Light component](./occurrence-components.md#light-component)) and having no children, is called an *empty occurrence*. For example, the function **Delete Empty Occurrences** finds all the Empty occurrences in the Tree and deletes them. | Empty occurrence | ![Empty icon](/api/media?file=/asset-transformer-studio/2026.5.0/media/STUDIO_PS-Icons_EmptyOccurrence.jpg)       |
| **Light Occurrence**    | An occurrence with a [Light component](./occurrence-components.md#light-component) is a `light occurrence`, or `light`.                                                                                                                                                                                                                                                                                                                                  | Light            | ![Light icon](/api/media?file=/asset-transformer-studio/2026.5.0/media/STUDIO_PS-Icons_LightOccurrence.jpg)       |

In the Product Structure, each occurrence type displays a different icon before its name:

![Occurrence icons](/api/media?file=/asset-transformer-studio/2026.5.0/media/NewItem181.png)

## About Icon color

Depending on its status, an occurrence's icon will be displayed in the Product Structure with a dedicated color:

* A cyan icon corresponds to an occurrence owning a prototype, and not expanded in the tree.
* An orange icon corresponds to an occurrence having children, and expanded in the tree.
* A gray icon corresponds to an occurrence not owning a prototype, and not expanded in the tree.

## Related Topics

* [Occurrence Components](./occurrence-components.md)