Rails Multi Table Inheritance, Polymorphic association or Single Table Inheritance?

I am trying to implement the OpenEHR reference model in Rails (ActiveRecord), but I am finding some problems as it works with many different classes,

Here is the Composition chart :

As you can see, many classes "inherit" an attribute pair from Locatable

or Pathable

* (the whole reference is huge and almost every class inherits from it).

Also, it sets data_types like other classes, for example in the same composition class, language

is a class CODE_PHRASE

that has two attributes ( link ).

Therefore, I am facing two problems: 1) how can I inherit attributes from abstract classes, and 2) how can I "include" the "needed" classes.

For the first problem, I was thinking about using polymorphic associations.

For a second I thought about using the STI, but quickly find a set of almost similar models (they are actually the same): CompositionLanguage

, CompositionTerritory

, EntrySetting

, EntryEncoding

, that I use only attribute type

to "back links", for example: the composition class can have up to three attributes CODE_PHRASE

as all three links have a different attribute (language, scope and category), I thought I needed to know for associations (it makes no sense to know that a composition has 3 code_phrases, but I didn't know which one is the corresponding attribute). On the other hand, a class Entry

has an attribute setting

and encoding

( link ).

I understand there could be different approaches, but I'd really like to know if it might not be Rails (or ActiveRecord) for this. Or maybe I am missing conceptual information.