NavigationPropertyBindings are used to assign an entity set to a Path ending in a non-containment navigation property. The assigned entity set can then be the target for annotations like Aggregation.CustomAggregate (see https://issues.oasis-open.org/browse/ODATA-1382).
Paths ending in a containment navigation property, which implicitly define an entity set, are treated totally different, however. In order to define a custom aggregate on this implicit entity set, the annotation Capabilities.NavigationRestrictions with type Aggregation.NavigationPropertyAggregationCapabilities/CustomAggregates must be used.
I propose a "variant" of NavigationPropertyBinding that can be used with a Path ending in a containment navigation property and which do not specify a BindingTarget, but serve as target for annotations. This would make the NavigationRestrictions annotation obsolete and the example in #92 could be rewritten as
Instead of introducing a new element NavigationPropertyBindingVariant (working title), the existing NavigationPropertyBinding could be extended: The Target attribute is no longer mandatory, and if it is absent
- the Path must end in a containment navigation property
- the NavigationPropertyBinding can be the target for any annotation whose term AppliesTo="EntitySet" (no need to specify AppliesTo="NavigationPropertyBinding"). These annotations then apply to the implicit entity set defined by the containment navigation property.