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.