This relation is explicitly marked as composite in shema/__init__.py to ease the
case of simplified profiles, where we want data objects to appear as children of
archive unit instead of references as expected by SEDA 2. Doing this, we
introduced a bug in SEDA 2 profile generation where the target value (hence the
referenced data object) was also considered as the 'cardinality entity' (the one
defining the cardinality / annotation) for the associated XML element. This led
to using the data object's cardinality / annotation for the *reference* element.