The interesting thing about coming down from meta-grammars is that you see that any context free grammar can be described fully in terms of just concepts and attributes of those concepts (where the attributes may be of a primitive or custom data type or may relate to another concept). So, as you start to look at the traditional OO modeling trifecta of Object, Attribute and Relationship, the question is whether we need a separate concept called relationships or if we should just model them as a special type of attribute.

[More]