Bitshares can only create bitGOLD or bitSILVER, bitGOLD and bitSILVER can only create country backing currency, BTS can exchange BitAssets.
How the bitGOLD or bitSILVER is being create. The market can only go up or down an example Alice want to created bitSILVER and the price is 100BTS to 1silver at the time, Alice make a derivative contract 50BTS buy up and 50BTS buy down at the same time in the blockchain this the market can go up or down the contract is worth it 100BTS all the time no interest involved and Alice need to put 100BTS to secure this contract a bitSILVER is born. All contract is the same only volume of the contract not the same the price volume is at the contract create wallet. If the new price of the BTS is 50BTS to 1silver Alice can end his old contract using 1bitSILVER in her own wallet and make a new want at a lower price.
How bitUSD,bitCNY is being create. bitGOLD or bitSILVER is back by 200% of BTS so what the price of the gold or silver is the price of the currency. Then blockchain holding the bitGOLD or bitSILVER to back the bitUSD,bitCNY. And blockchain control the backing currency limit flow in and out of bitGOLD and bitSILVER.