Level B extended system all share the same namespace for their data. The schema mapping ensures that level B extensions will be processed properly by non-extended systems. Fine.
But what if one Level B extended system is connected to another system, extended with another Level B extension? Of course everything runs in the same namespace. As long as the sets of extended classes in both extensions is disjoint, this all may work well. But what if both disparate extensions have a non-empty intersection of classes? Then, the receiving system would receive an object of such a class and it might start to parse the content of the extension point of this object according to its own extended structure, whereas the supplier has filled the exntension point according to his - different! - extended structure. I assume this will in the best case cause a runtime error exception, which I find inacceptable in the light of the interoperability claim of DATEX II. The receiving system might be able to determine the potential conflict, by examining the schema for instance, but a standard should be strongler than to allow avoiding problems, it should ectually strive to force avoiding problems.
Duplicate with #83