Stefan Talmon: From the point of view of international law, this step is ineffective. The tribunal can only rule on questions to do with the interpretation and application of the UN Convention on the Law of the Sea (UNCLOS). The question is: Is this dispute between the Philippines and China really a dispute about interpretation and application? Even if this is the case, there exists the possibility for states to remove certain disputes from the jurisdiction of the international courts. China did this when it became a contracting party to the convention. Therefore, this dispute is not within the tribunal's jurisdiction. The Philippines' move is purely political.
DW: Can it be understood as a last resort?
Yes, I would call it a political call for help.
Relations between the Philippines and China have been strained since a standoff last April at Scarborough Shoal, which lies in Manila's exclusive economic zone but is claimed by China. China has said it will continue to send patrol ships to the waters. Is this step a legitimate and effective means of confirming its superiority?
Both sides lay claim to this group of islands. The fact that China currently controls it doesn't mean it has a legal title of sovereignty to the islands. At the moment, China has de facto control but this is disputed by the Philippines.
The convention does not deal with the question of whom the islands belong to. This is a matter of general international law. A solution can only be found via negotiations. Unless, China explicitly recognizes the UN's jurisdiction.
What would happen if the Philippines were to not do anything?
The Philippines need only to protest against China's control of this island area. This alone suffices to hinder China's claim. Even if China were to control the islands for the next 50 years and the Philippines were to simply repeat over and over again that the islands are theirs, this would be enough for the question to remain open in legal terms.
Does this also hold true for the Senkaku Islands which both Japan and China lay claim to?
Yes, Japan has control of them and China protests this. This was clear when the Japanese government bought three islands from private individuals, and China said they could not buy them because they are not Japan's islands to buy but China's.
This is why it cannot be decided whether these islands belong to China or not?
Exactly. China has a problem in that it often argues one way when talking about its own claims and in another when other states use the same arguments for their own claims. Both sides use and reject the same arguments. That's why in the end it's an objective, legal situation. One question has to be clarified: Whom do these islands belong to? And this is a matter of general international law. Who has the title? On the basis of discovery, conquest or administration. And does any other state lay claim to the territory? Each case has to be examined on its own merits. Even if China, Japan or the Philippines have patrol boats or station troops in a territory, this does not give them the title so long as another state lays claim to the same territory. The fact that the Philippines have now filed an arbitration case against China is a public comment on China's claims to the island group.