This system is a departure from traditional accounting. A central feature of the system is the use of an events database. Traditional accounting records may not exist perse. For instance, in this example the sales invoice file replaces the sales journal and AR-SUB ledger. Total sales is the sum of all invoices for the period. Summing the open sales invoices (those not closed by cash receipts or credit memos) provides accounts receivable information. In theory, such a system does not even need a general ledger because sales, sales returns, accounts receivable-control, and cost of goods sold can all be derived from the invoices in the events database. Most organizations, however, prefer to maintain a separate general ledger file for efficiency and as a cross check of processing accuracy.