Every trading partner has their own unique EDI requirements that are described in their EDI guide. You must have the trading partner's EDI guide in order to accurately read an EDI record. The EDI guide explains which segments and elements are mandatory, conditional, and optional as well as the values that may be used for each element. The example below is an excerpt from the EDI Guide for Tractor Supply. Note that the N1 element from the previous page, a qualifier, is explained.
N1 - NAME, Purpose: To identify a party by type of organization, name, and code
|REF. DES.||DATA ELEMENT NAME||ATTRIBUTES||VALUE & COMMENTS|
|N101||ENTITY ID CODE||M||"BY" = Buying Party|
|N103||ID CODE QUALIFIER||C||"92" = Assigned by Buyer|
|N104||ID CODE||C||"0" + 3-digit TSC store/DC code|
An EDI guide will also frequently contain general guidelines for transmissions, procedure for testing and moving to production, and contact information. Additionally, an EDI guide will specify which standards the trading partner uses. You should always consult with a trading partner's EDI guide for the precise interpretation of their EDI transactions.