When I began working at Aquamor, formerly TST Water, I had no idea that EDI even existed, let alone what it was. It wasn't in the job description. The previous developer had built an intranet website in ASP VBSCRIPT he called EDI and I figured that part of my task might be to update the website to maybe a more modern version. I was wrong. EDI is sort of an old markup language or document model that is used like a SOAP API. The data is sent as a text file sent either via (s)FTP or basically over an email protocol network as an attachment.
The actual EDI files were parsed using his custom code written in Visual Basic 6. Luckily I had enough experience in VB6 to help him maintain and eventually take over.