[DDI-SRG] Inclusion of an existing CodeScheme into a hierarchical coding structure

[Joachim Wackerow]

I see a requirement of an inclusion of an existing coding scheme into a 
hierarchical coding structure. Use case:

Building a total for all ISCO occupation codes for a ncube. ISCO has 
four nested levels in a hierarchical coding scheme. It doesn't include a 
code for the overall total. An overall total can make sense when using 
ISCO in a ncube. A new code for the total can be invented. All the ISCO 
codes must be nested below this top-level code. This is currently only 
possible by copying the whole ISCO coding scheme to this place. It isn't 
possible to include by reference an existing code scheme at the code 
level. This is currently only possible on the coding scheme level.

The suggestion is to add a choice below code (code or a reference to a 
coding scheme) instead of just a code (like now).

The whole structure of CodeSchemeReference below CodeScheme can be then 
used below Code in alternative to a nested Code.

Example:

<l:Code levelNumber="1" isDiscrete="false">
   <l:CategoryReference>
     <r:ID>ISCO_total</r:ID>
   </l:CategoryReference>
   <l:Value>10000</l:Value>
   <CodeSchemeReference>
     <r:ID>ISCO_CodingScheme</r:ID>
   </CodeSchemeReference>
</l:Code>

The code with the value 10000 represents all nested codes, here all 
codes existing in the ISCO coding scheme. This is here the overall total.

The CodeSchemeReference allows also to restrict the included coding 
scheme by levels or codes.

When this would be possible the question raises, are the levels still 
appropriately numbered. The documentation on levelNumber of Level says: 
"Designated identifier for the level; generally increases as the level 
of indention for nesting increases". This is not really clear: is it 
just an identifier or is it a ranking number system?

In the case of an identifier it would not cause a problem. In the case 
of a ranking number system the top-level code has to have a lower level 
number than the level below. Then it would be more flexible to invent a 
element which reassigns new numbers to existing coding schemes.

Overall it seems to be easier just to change the documentation in terms 
of clarity that it is just an identifier and that - if using increasing 
numbers - this wouldn't express some actual hierarchy.

Any comments?

Achim