The e-book linked here is provided by GXS - actually by GXS' new entity, OpenText. We've watched the transition of GXS over the years, and more recently seen its acquisition by OpenText, and look forward to even more substantive contributions from the company. But for now, I suggest you take a look at this e-book "EDI Basics" by Rochelle P. Cohen. At 40+ pages it's longer than the typical e-book and provides a nice overview from the most introductory levels. 

You may even find some interesting tidbits about EDI that, while you've been working in the field for several years, you didn't know. For example here's a short quote: "In the 1960s, the railroad industry, which needed to find a faster and more efficient way to communicate information about goods being transports, began to send this data electronically." Sounds to me as if not much has changed other than the range of trading partners has expanded tremendously and the complexity of the data has exploded.

Even if you intimately familiar with the nuances of EDI and could write your own e-book, I suggest you take a look at this one... you may be inspired to create your own (we'll be happy to publish it for you). Know in advance that you will have to provide your contact information in order to access this book, but it's painless, and a good read.