The relational model is to data what Lisp is to code: despite attempts to beat it, nothing really can because all those other models are expressible in terms of it (and, usually, can be made very efficient in practice).

RDBMS and Lisp sit near the tao of their respective domains, which is why I advise people to stick with an RDBMS unless they have a really, really, really good reason not to. Or as Nik Suresh put it, "Just use Postgres. You nerd. You dweeb."