Ownership of an island 500 years ago really means ..nothing. The Ming Dynasty is not PRC in any case. Arguing that China owns Diaoyu is like arguing that the Italians own all of Europe and a good deal of North Africa because it was all under control of the Roman Empire. The Roman Empire doesn't exist anymore, and neither does the Ming Dynasty. China does, and so does Japan. I remind you that I say this because I haven't read that article, since it's rather long, and I'm rather slow at reading Chinese.