Hi Gady,
Another (much lighter) way of doing this is with the 'serliaze'declaration, that serializes hashes or arrays automagically.
class Element < ActiveRecord::Base serialize :variables end
Then you can just do setters with:
element.variables = {:price => '4', :availability => '7 Days'} element.save
And the getter becomes: element.variables[:price]
This way, you don't need additional classes, tables or relationships.
Matt