In every EDI application, knowledge of the business needs and functions is of paramount importance. If you don't understand a "purchase order" or a "load tender" or a "health care claim or encounter" you'll never be able to map the ANSI or EDIFACT EDI data format for these transactions. In my experience, logistics is the toughest because of the many, many unrelated (by ownership) parties who need to be in the loop.
In reviewing the business elements of a company that interfaces with EDI, I am certain the most difficult to understand is the “Supply Chain”. The most common mistake is thinking that “Supply Chain Management” (SCM) is just another name for “Logistics”.