Partner navigation property of an uplink defines collection, but only for one level

[HeikoTheissen]

If composition of entities is expressed through containment navigation properties, every entity type can have an uplink non-containment navigation property that addresses its parent in the composition hierarchy. Partner navigation properties can then be used to define the collection that contains the navigation target.

For every composition A -> B there is a pair of navigation properties:

<EntityType Name="A">
  <NavigationProperty Name="B" Type="Collection(ns.B)" ContainsTarget="true" Partner="uplink" />
</EntityType>
<EntityType Name="B">
  <NavigationProperty Name="C" Type="Collection(ns.C)" ContainsTarget="true" Partner="uplink" />
  <NavigationProperty Name="uplink" Type="ns.A" Partner="B" />
</EntityType>

If a resource path $P$ identifies an entity of type A, then $P$/B(key)/uplink is the same entity as the one identified by $P$.

If would be good if this also worked for uplinks that go up more than one level:

<EntityType Name="C">
  <NavigationProperty Name="uplink" Type="ns.B" Partner="C" />
  <NavigationProperty Name="upuplink" Type="ns.A" Partner="B/C" />
</EntityType>

But Partner="B/C" is not allowed according to OData-CSDL, section 8.3

The path MAY traverse complex types, including derived complex types, but MUST NOT traverse any navigation properties.