computer.rb

require_relative 'ds'

class Computer
  LIMIT = 100    # if price exceeds this, the description will be flagged
  FORMAT = "%s%s: %s ($%d)"     # flag, name, info, price.

  def initialize(computer_id, data_source)
    @id = computer_id
    @data_source = data_source
  end

# I don't know if #send or #method missing is better, but this demonstrates both.
  
  def method_missing( item )
    info = @data_source.send "get_#{item}_info", @id
    name = item.to_s
    price = @data_source.send "get_#{item}_price", @id
    flag = price >= LIMIT ? "* " : ""
    # result =  # unused name for return value
      FORMAT%[ flag, name, info, price]
  end  

end

ds = DS.new
workstation1 = Computer.new(1, ds)
p workstation1.mouse
p workstation1.cpu
p workstation1.keyboard

Good point, A whitelist of items would be a good addition, But for now, those errors will be caught by DS::method_missing.
Do we know that DS has implemented *_info and *_price in pairs?
Or would we want to test respond_to? for both?
It hasn't implemented the id aspect very well.