class Manufacturer < ActiveRecord::Base
  has_many :models

  validates_presence_of :name
end

class Model < ActiveRecord::Base
  belongs_to :manufacturer
  has_many :motorcycles

  validates_presence_of :name
end

class Motorcycle < ActiveRecord::Base
  belongs_to :model
  belongs_to :owner

  validates_presence_of :vin
end

class Owner < ActiveRecord::Base
  has_many :motorcycles
end