The Japanese Government took measures for the territorial incorpotation of Dokdo by Cabinet's decision and Notification 40 of the Shimane Prefectural Government(島根縣告示 第40號) in the year of 1905, alleging that the islets were terra nullius. But this kind of Japanese assertion is groundless. It's because almost all the official documents ever produced and found in Korea and Japan have shown that Dokdo belongs to Korea and the Korean Central Government manifested her territorial sovereignty over the small island by Emperor' Edict No. 41 declared and published in the government gazette on 25 October, 1990 before the Japanese local authorities' territorial measures were worked out. Besides, the Shimane Prefectural Notification No 40 contained substantial problems in procedure for the acquisition of territory, in that it was neither published in the central government gazette nor communicated to relevant countries, including Korea, China and the U.S.
Later on, Japan changed territorial argument or claim over Dokdo on the basis of terra nullius, insisting that the islets were undoubtedly an integral part of Japanese territory in the light of historical facts and international law. But this changed position cannot be lawfully sustained under international law according to the general principle of estoppel.
Proving territorial sovereignty over Dokdo is one of the major practical tasks for the Korean international legal scholars. We must find logical inconsistencies in the Japanese literatures or declarations on territorial claim over Dokdo. Further, we should upgrade studies on Dokdo, synthesize and systematize the drawn results from raw materials in order to intensify Korean territorial claim over the island. Finally, It is very important to make public the Korean legal ownership of Dokdo, far and wide, on domestic and international level as well.