After hard negotiations, China and Japan have reached an agreement to jointly explore part of the gas deposits in the East China Sea, thanks to the efforts of consolidating bilateral ties between them.

For common people, a historical background on the East China Sea issue is indispensable to understand the strategic significance of the agreement in promoting a new kind of Sino-Japanese relations. And such knowledge would also help allay misgivings that this agreement would harm China's sovereignty.

Similar with the disputes among other coastal countries over marine territory, that between China and Japan for their competing claims over the East China Sea focuses both on the sovereignty to the sea and the economic benefits from the rich reserve of gas and oil.

Since a large reserve of gas and oil was discovered in the East China Sea in 1968, the Sino-Japanese dispute over it intensified. As both countries rely heavily on imported energy products, neither of them would easily drop its claim. The disagreement was so severe that it could endanger bilateral ties if not dealt with properly.

Therefore, the authorities from China and Japan have realized it is now time to settle the problem with mutual efforts for the disputes might escalate and result in a historic retrogression in their ties. And such a possibility would not be welcomed by politicians with foresight and wise people in both countries.

There are two international laws to be referred to when neighboring countries divide marine area, the Geneva Convention of the Continental Shelf signed in 1958 and the 1982 UN Convention on the Law of the Sea.

The second convention, to which China and Japan are signatories, stipulates that the continental shelf of a coastal state comprises the seabed and subsoil of the submarine areas that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin.

China has always held that the Okinawa Oceanic Trough, 2,700 meters deep, should be regarded as the point that divides the continental shelf with Japan because it extends from the Chinese continental shelf.

Meanwhile, Japan claims that the East China Sea should be demarcated along a "median line" with equal distance to the territories of the two countries.

Since there are international precedents for the claims for both countries, neither of them would compromise their rights over the marine territory. Many conflicts rise from the dispute and become a bitter part in the bilateral ties.