The format for XML schema is well defined and does allow arbitrary attributes to be added. You can add annotations but this mechanism is cumbersome and it also means schemas exposed by UA servers need to have custom UA modifications added to them.

After a discussion with Randy I want to change my proposed resolution of the problem.

Instead of changing the OPC Binary Schema I want to propose to add a new optional Property to the DataTypeDictionaryType. This Property would contain an array of structures with an entry for every data type in the dictionary. The structure will contain the data type name, the data type NodeId and the Encoding NodeId.

This does not change the OPC Binary Schema and would also work for the XML or other encodings.

It is just an optional Property for optimization but everything would also work if it is not available.

We need to move this issue to Part 5 for this change

Added proposed changes to document OPC UA Part 5 - Information Model 1.03 Draft 11_RedundancyChanges.docx posted in Meetings -> 2015 -> 2015-02-23

Did not agree on solution yet

fixed in 1.04.00 by adding attribute to DataType Node (in Part 3 - version 1.04.02) and move old approach to annex.

Agreed to edited changes in San Ramon meeting.