First, we give a brief overview of the traditional public ledger accounting models and then discuss the private UTXO model and how to modify it so that we can integrate with ERC20 tokens and other smart contracts. Ledger Models To store value on a distributed ledger, we have two standard data structures at our disposal: Account Model: a map from a set of accounts to a set of balances UTXO Model: a set of claims that represent unspent transaction outputs Account Model The account model is the simplest of the two and the one that should be familiar to most people. Consider three people, Alice, Bob, and Charlie, who keep a ledger between them: