How assets are backed?

[Bangzi]

Smartcoins - Back by Bitshares core token BTS such as bitCNY, bitUSD, HERO

User Issued Asset (UIA) - Back by Credit of Issuers such as OPEN.XXX, GDEX.XXX, RUDEX.XXX and they may or may not have equivalent coins at the native wallet.

[TreantBG]

Hello,

i read a lot about this topic but i'm still little confused
can you please explain a little bit more

my question is how assets are backed and who owns the coins?
can exchange touch the backed coins?
and how to convert the asset to its original value?

for example OPEN.BTC its btc backed asset
so open ledger have their own BTC wallet that stores that 1:1 backed asset right?
can open ledger access this wallet to make transactions?
And how can i use the BTC value or the value of any coin backing this asset OPEN.X or BRDGE.X without withdrawing from the exchange?
for example there is a new exchange that issues EXCHANGE.BTC and they close cuz are scammers or something else.. is it possible to take the BTC value back ?