gistfile1.rb

# app/models/physical/organisation.rb
module Physical
  class Organisation < ActiveRecord::Base
    validates :foo, :bar, :baz, :quuz
  end
end

# app/models/physical/user.rb
module Physical
  class User < ActiveRecord::Base
    validates_presence_of :email_address, :name, :this, :that, :other
  end
end

# app/models/logical/organisation_user_manager.rb
module Logical
  class OrganisationUserManager
    USER_PERFORMANCE_BOUNDARY = 100

    def initialize(organisation)
      @organisation = organisation
      @users = organisation.users.to_a
    end

    def add_user(user)
      @users << user
    end

    def okay?
      @users.size < USER_PERFORMANCE_BOUNDARY
    end

    def save
      @organisation.users = @users
    end
  end
end