Quite a long time since I last posted.
We arrived to a messy propietary database.
We thought Llblgen could help us building a proper logical data model on top of the physical one (no FK, not even PK in some cases, ... )
We created a Target per entity hierarchy with an abstract parent entity and two children entities.
The discriminator field is a boolean where each value (true/false) is assigned to one of the children entities.
However, it gives an error on parent entity as no discriminator value is set), but none is required (is abstract) and none can be assigned (null is not valid, true/false are already taken).