Proposal that we remove the "has" elements from DITA 2.0

[Kristen James Eberlein <kris@eberleinconsulting.com>]

I propose that we remove the following elements from DITA 2.0:

• hasInstance
  
• hasKind
• hasNarrower
  
• hasPart
• hasRelated
• relatedSubjects

Reasons for removing them:

• We are not clear on the distinction between <hasRelated> and <relatedSubjects>.
• I don't think these elements are much used, and they clutter up subjectScheme maps. I've constrained them out of every subjectScheme shell that I've created.
  
• We do not have an expert on the TC to maintain these elements.

If anyone needs them, they could easily create a domain specialization and integrate it into their document-type shell for subjectScheme. They could be added to the GitHub repo for specializations removed from the DITA standard.

--
Best,
Kris