No way to reuse external namespaces (and their objects) in schema mapping

The current mapping of DATEX II to XML schema definitions (XSD) does not support importing other namespaces, since the schemaTypeInclude tagged value does allow providing a bespoke schema definition for a datatype (as used for example for the MultiLingualString class) but this definition is just put as some kind of text macro at the place where the tool would introduce its own type definition if a standard mapping mechanism had been sued instead.

Unfortunatley reusing data structures from external specifications usually also requires importing external schemas and declaring their namespaces (see http://www.w3.org/TR/xmlschema-0/#import). SInce there is no way in the mapping that specifies how to create the required namespace declarations and import elements, such use of external schemas / namespaces is not possible.

Proposal: Include mechanisms in the XSD mapping to trigger creation of namespace declarations and schema imports.

Use Case: the issue appeared when trying to include an XMLDsig signature into a model extension. This was not possible since there was no way to declare the

http://www.w3.org/2000/09/xmldsig#

namespace and include the corresponding schema.