It's entirely possible that I'm simply not familiar enough with the nuances of the term in this context to to get it, but the phrase suggested to me both the select-includes-subclasses behavior that you mentioned above (and that is explicitly discussed in the spec) and that an entity could have a relationship to an instance of another entity type that was inherited from a superclass.

As a slightly-less-hackish workaround from the OO side, is there a way to duplicate the relationship field on the subclass such that it always points to the same foreign entity as the relationship field on the superclass (so that Customer could have the collection of AbstractOrder but also a collection of RegularOrder that contained all of the RegularOrder objects in the first one)?
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