JT on EDM

I saw this piece on DSL and MDE, necessary assets for Model-Driven approaches and it made me think about DSLs. First, here’s the definition of a DSL from the article
DSL is a programming language or executable specification language that offers, through appropriate notations and abstractions, expressive power focused on, and usually restricted to, a particular [...]

I got an interesting series of questions from a reader that seemed to me to justify a longish post. The initial question was quite harmless looking:
Can you give a clue as to what software engineering approach you use/recommend for EDM, but especially business rules that non-IT staff can alter safely?
But the whole thing got more [...]