XMI12 — Why do we need 3 XMI DTD rulesets?

The XMI spec currently defines 3 rulesets for generating DTDs for
meta-models. The rulesets give different DTDs, but they are all intended
to match (i.e. be capable of validating) the document production rules
in Chapter 9.

Given that the 3 kinds of DTDs are equivalent, why do we need them all?
The point of XMI is the interchange of metadata, not the generation of
pretty DTDs. Indeed, the XMI DTD compliance section (11.2.1) makes
it clear that any DTD that expands to the same form is compliant.

I suggest we just delete the compact DTD rulesets, and leave the
implementation of "pretty" DTDs as an exercise for the implementor
to undertake ... or not. The alternative is that we must ensure that
any changes / corrections are made to the simple ruleset are made to
the other two rulesets.

Remove DTD rule sets 2 and 3 in chapter 4