> For the complete documentation index, see [llms.txt](https://umber.gitbook.io/umber/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://umber.gitbook.io/umber/concepts/virtual-collections.md).

# Virtual Collections

Sometimes you need to group several assets together and reference them as a single unit — **Collections** are built for that. A collection can hold one asset type or a mix of types.

A common example: a product on an e-commerce site, where the product has multiple images, a 3D model, videos, PDFs, and JSON spec data. Grouping these together makes them far easier to fetch and manage consistently.

## Structure

A collection has two parts:

* **Definition** — the collection's ID, name, and other attributes
* **Items** — the actual files, which can be of various asset types

The Collection ID is a unique slug of letters, numbers, hyphens and underscores, up to 50 characters, and can't be changed once the collection exists. `actions` is reserved and can't be used.

## Characteristics

* A collection can contain multiple asset types, or be restricted to specific ones.
* The number of items is limited to a service-configured ceiling, currently **5,000** per collection.
* Collections do not have versions (unlike individual Virtual Assets).
* A collection can be tagged to a specific platform.

## Examples

* Product images, videos, and PDFs on an e-commerce site
* Tutorial videos, transcripts, and questions on a learning platform
* Game assets bundled for a specific release

## Deploying a collection

A collection is deployed to an environment as a single unit and is Live, Offline, or not deployed there — the same three states an asset version has. Since a collection has no versions, there's no "which one is default" question to resolve: a collection has one Live pointer per environment, full stop. See [Deployment States](/umber/concepts/deployment-states.md) for how this compares to asset versions.


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