The app will keep track of available USD to trade as well ass their current balance in each cryptocurrency and their overall value in combined USD.
Real time market prices will be used in real time from various market APIs (ex: blockchain.info API)
user_table: -username has_many: transactions
account: -user_id: foreign_key -usd: decimal -btc: decimal
belongs_to: user
transaction table: -user_id: foreign_key -usd_change: decimal -btc_change: decimal -approved: boolean