Ok, now think this the rest of the way through. Without FKs, how do you, at the application level, ensure that A and B don't commit separate changes (A to chil

Ok, now think this the rest of the way through. Without FKs, how do you, at the application level, ensure that A and B don't commit separate changes (A to child, B to parent) that break consistency? If A tries to insert a child for 1, and B changes the id to 2.... OOPS! And from both's perspective it looks perfectly safe.