Denormalizes provides a clean syntax for specifying observation
and denormalization rules between ActiveRecord models.

  class UserScore < ActiveRecord::Base
    belongs_to :user
    named_scope_for :user_id

    denormalizes :score, :from => :user
  end

There are a number of common-sense conventions in use here.
First, the denormalization model must have reflection onto the
observed model in the form of a has_one or belongs_to.

Second, denormalized values can only be activerecord attributes
of the observed model, (must be columns in the database) and
the observer model's columns must match those of the observed
model.