> For the complete documentation index, see [llms.txt](https://docs.imerit.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.imerit.net/labeling/labeling-tools/relation.md).

# Relation

Relations connect annotations to describe how they are associated. Ango Hub provides two relation types:

* [Single Relation](/labeling/labeling-tools/relation/single-relation.md), which connects two annotations and can include a direction.
* [Group Relation](/labeling/labeling-tools/relation/group-relation.md), which groups two or more annotations.

Both relation types can contain [nested classifications](/labeling/labeling-tools/tools/nested-classifications.md). This lets project managers ask questions about the relation itself, such as the type, confidence, or context of the connection. Relation classifications can be required, can contain conditional follow-up questions, and are included when annotations are saved, imported, exported, or sent through a webhook.

Relation classifications are available wherever relations are supported, except in 3D MSFT projects and the DICOM series editor.