Currently NavigationPropertyPath expressions must end with a navigation property name, and PropertyPath expressions must end with the name of a structural property.

On the other hand annotations add "virtual (navigation)properties", so a NavigationPropertyPath expression could as well end with an annotation of type Edm.EntityType or any concrete entity type (or a collection of these), and a PropertyPath expression could end with an annotation of types Edm.ComplexType, Edm.PrimitiveType, or a concrete primitive type, enumeration type, or complex type, or a type definition (or a collection of these).

An example for "virtual navigation properties" is given in https://tools.oasis-open.org/issues/browse/ODATA-278 . The aim was that we can use "virtual navigation properties" (and "virtual properties") also as a NavigationPropertyPath (and as a PropertyPath ). Currently the expressions
<PropertyValue Property="NavigationPath" NavigationPropertyPath="@ACR.Supplier" /> and
<PropertyValue Property="NavigationPath" NavigationPropertyPath="@ACR.PurchaseOrders" />
in the example are invalid, because the NavigationPropertyPath expressions must end with a navigation property name.