Structure

An EDI file contains a structure known as enveloping.

Enveloping is the way EDI ensures file integrity and lets the message determine its destination and type.

This figure shows an X12 EDI structure example.

Based on the figure, we see that:

The interchange is the basic unit of an EDI file. Several interchanges can be bundled into a single file for data transfer.

An interchange starts with an interchange header (ISA) and ends with an interchange trailer (IEA).
A functional group is a group of similar transaction sets which have the same functions.

A functional group starts with a function group header (GS) and ends with a functional group trailer (GE).
A transaction set contains the information required by a receiver to perform a standard business transaction.

A transaction set starts with a transaction set header (ST) and ends with a transaction set trailer (SE).
Data segments are used to make up transaction sets. Data segments are roughly equivalent to a single line on a document. Data elements contain the basic units of information and are used in various combinations to make up data segments.