Updated: Jun 3, 2019
DEX is the process where the grocery retailer is able to electronically receive a Direct Store Delivery (DSD) invoice at the time of delivery at the back door receiving area. The reason for DEX is with true DSD deliveries, the sales rep does not know what will be invoiced until they arrive at the store and see what is left on the shelves. This eliminates the possibility of sending an electronic version of the invoice prior to the delivery arriving. The benefit of DEX are many, most being on the retailers side, which include elimination of manual data input, being able to automate the checking of prices, authorized products, authorized vendors, updating inventory in real time and validating UPCs to make sure unknown items do not get to check out.
The alternatives to DEX is sending some form of data file from vendor to retailer post delivery. There are many disadvantages to doing this. Since the file is being sent after the fact, maybe hours, maybe days, maybe weeks, maybe not at all, its much harder and maybe impossible to know if the data accurately reflects what was delivered. You could also end up with unauthorized or unknown products on the shelf or worse yet getting to checkout. Additionally there might be time limits for invoice payment, as is the case with alcohol in some states, that may not be met when invoice data is sent post delivery. One of the biggest problems is whatever method is being used to send the data, it almost certainly will not be some form of industry standard that will work with any vendor and any retailer. Imagine the nightmare of each trading partner requiring a different data file format to exchange data.
There is a reason all of the large major retail grocers use DEX.