I gave you Liquity as an example. They don't have "books", it's a smart contract which takes ETH as a collateral and lets ppl to borrow LUSD against it. Maker

I gave you Liquity as an example. They don't have "books", it's a smart contract which takes ETH as a collateral and lets ppl to borrow LUSD against it. Maker initially worked same way, but eventually they started accepting off-chain collateral.