> Should the implementation throw an error in such situations, warning the > user of the erroneous metadata?
Shared FK relations are a perfectly valid thing to have IMHO http://www.datanucleus.org/products/accessplatform_1_1/jdo/orm/one_to_many_collection.html#shared_fk You could have the same as that example with 1-1 and a discriminator for determining the relation. The place of an ORM spec is to standardise particular relation types, not to prevent other ones. -- Andy (DataNucleus - http://www.datanucleus.org)
