Some have questioned whether these criteria are enough, as they allow less-recognized entities like the Republic of China (Taiwan) or under- or unrepresented entities like the Principality of Sealand, Somaliland or Liberland to claim full status as states. According to the alternative constitutive theory of statehood, a state exists only insofar as it is recognized by other states. It should not be confused with the Estrada doctrine.