They were -- I'm guessing here -- trying to develop their own Document Object Model. Distinct from any established DOM. The Wikipedia entry on DOM provides several examples of existing DOM's. Why reinvent?
The application is -- ultimately -- going to be in Python. There are two candidate DOM's that could have been used: the XML DOM and the RST DOM as implemented in Docutils nodes module. Instead, they were reinventing: they appear to have spent a great deal of time writing use cases for "editor". I expect there was a use case for "wheel" and "fire" in there also.
What scared me was the "flatness" of the model. Every buzzword had it's own class. There was no inheritance or reuse anywhere in the diagram. Parts of the model where influenced by the DocBook schemas. The actual DTD could have been turned into the model, but wasn't.
Further, undefinable terms like "sentence" showed up as class definitions. XML's DOM treats all text as -- well -- text. Any language structure is outside the DOM. RST, similarly, treats text as a container "
... children are all `Text` or `Inline` subclass nodes."
All I could suggest was "locate common superclasses" and "until you can define 'sentence', omit it". And then run outside and gouge out my eyes.
It's hard to criticize something like that in a truly helpful manner. Fixing the model is merely putting lipstick on a pig.
As far as I can tell, the application is -- somehow -- an editor that imposes a severe set of structural constraints on what the author can do. It's as if RST, docutils and Sphinx don't exist. The real solution isn't "fix your object model" it's "fix your problem statement and learn RST."
Check out this reply:
The advantage of having an "outliner data model" and a "document data model" like DocBook XML is that your outliner functionality is not limited by the DocBook XML. The downside is that have to create and support a second model as well as provide a mapping between the two.
In other words, rather than simplify, we'll (1) insist the eye-gougingly bad model is "better", (2) justify the complexity ("not limited by DocBook [DOM]") by and (3) plan to add some more complexity to map an overly complex (and atypical) DOM to a standard DOM.
Not a very parsimonious approach to design.