Enterprises developing invoices must use commodity unique codes; the party receiving the invoice must provide a taxpayer identification number; tax experts say that the taxpayer identification number of an enterprise is like the ID number of an ordinary person, and is the strongest catch in the era of big data on invoice information. The enterprise's invoice must have a taxpayer identification number before it can be used as a legal tax voucher, which means that the data system based on the taxpayer identification number has been established, and all the flow of invoices for the enterprise's sales and purchases are clearly seen in the tax big data system.