7.3.4. Sub-Collection Relationships
A sub-collection relationship defines a hierarchical link between a resource and a sub-collection. The sub-collection exists or has some meaning in the context of a parent resource. For example, a virtual machine contains network interfaces, which means the API maps the relationship between the virtual machine resource and the network interfaces sub-collection.
The API defines a relationship between a resource and a sub-collection using the link rel=
attribute: