class LicenseAcceptance::ProductReader

def lookup(parent_id, parent_version)
  parent_product = products.fetch(parent_id) do
    raise UnknownProduct.new(parent_id)
  end
  children = relationships.fetch(parent_product, [])
  if !parent_version.is_a? String
    raise ProductVersionTypeError.new(parent_version)
  end
  ProductRelationship.new(parent_product, children, parent_version)
end