X12 Structure

To better understand the reason X12 format is what it is we need to understand a bit of the history. X12 was originally developed at the time when due to the limitation of technology when the need of every byte of information was carefully considered. As a result readability was sacrificed for smaller size. The modem speeds of the day were measured in bits (300 to 1200 bit/s being the latest and greatest)

At the same time communication between companies was not very reliable. A dropped line could easily create lost of data. The X12 standard defined a document structure that ensures the accuracy of data. The enveloping used in X12 allows the receiving party to validate that all transmitted segments have been successfully received.

Bellow you can see how the X12 document is organized. The section bellow depicts the structure of the document as it is send or received to/from the trading partner via Value Added Network (VAN).

 +-[ISA] INTERCHANGE CONTROL HEADER
 |
 +---[GS] FUNCTION GROUP HEADER
 |
 +-----[ST] TRANSACTION SET HEADER
 |
 +------- (...)
 |
 +-----[SE] TRANSACTION SET TRAILER
 |
 +---[GE] FUNCTION GROUP TRAILER
 |
 +-[IEA] INTERCHANGE CONTROL TRAILER
					

In Interchange can contains multiple Function Group envelopes, and each Function Group envelope can contain multiple Transaction Sets. Each transaction set represents a document (order, invoice, ASN).