Collision of types hasn't been a problem so far so it seems easier to just leave them all in the same namespace, especially since they share a bunch of common types in the same namespace.
Instance documents can conform to any of the valid schemas/DTDs for the given document name; I don't see that the namespace for one of the schemas makes any difference to that. You have to read the document enough to know which of the schemas/DTDs it should conform to before you can validate it.
Gunnar Morling wrote on 02/24/2013 12:01 PM:
[javaee-spec users] Re: Java EE 7 schemas