we change the meaning of collection role as it's unqualified here and it's qualified in ORM: I don't like this idea even if I don't have a strong argument against it;

Well, an argument would be great Also, it is not completely unqualified. The comparison w/i TypeMetadata is ignoring the class, but we still look up the right DocumentBuilder and TypeMetadata before hand.

the regexp approach is too fragile: if you have the collection named collection1, it's going to match MyClass.collection1 MyClass.object.collection1, my.package.name.unfortunately.contains.collection1.MyClass.property and so on.

Not sure whether this is really the case, but we can add some tests.