If a navigation property leading to a related entity type has a partner navigation property that specifies a referential constraint, then those key properties of the related entity that take part in the referential constraint MAY be omitted from URLs. Example: Order contains OrderItem, key of Order is ID, key of OrderItem is OrderID and ItemNo, with a referential constraint tying the value of the OrderID key property of the OrderItem to the value of the ID property of the Order. Then the following URLs are equivalent: ~/Orders(1)/Items(OrderID=1,ItemNo=2) ~/Orders(1)/Items(2) If the constrained key part is specified then it MUST match the parent. If the key is included in the content it must be ignored. This should apply any time there is a referential constraint Accepted: https://www.oasis-open.org/committees/download.php/48481/odata-meeting-28_on-20130307-minutes.html#odata-264