An EDI transaction set, X12 Purchase Order (850) in this case, is segmented into an interchange control, functional groups, and transaction sets. These can be thought of as the envelope containing the sender/receiver information needed for the document to be sent, similar to the addresses on an envelope. The transaction set envelope contains segments and data elements, which describe the information within the transaction. In this case, we have a single PO with three items being ordered.
This is a simple example of EDI. Documents are usually more complex and can contain multiple functional groups and transaction sets. ASC X12 governs hundreds of transaction sets within several industries including Communications, Finance, Transportation, Supply Chain, and Insurance. Although they must conform to standards, individual implementations vary by industry and trading partners. For example, Walmart and Target are in the same industry, but their EDI implementations have been customized to fit their specific needs.