First Step in Learning EDI (based on my experience)

I still remember many years back, when i first introduced and learning EDI stuff, standards, messages, and what EDI is all about. Throught Mr Google, 2 main resources helped me a lot. 1st is tutorial  documents from GXS  website, 2nd is EDI message hierarchy structure information from stylusstudio.com.
Now many years later, when i check again those documents from GXS, those old faithful documents still are there. Look like the front page cover in the pdf changed, and i believe the contents still pretty much the same. Unfortunately i no longer have old tutorial documents to compare what are the changes.
Anyway, i uploaded these 2 self-learn-proven tutorials that i download from GXS website:
ANSI ASC X12 Standards Overview Tutorial
EDIFACT Standards Overview Tutorial
Once you get an general idea about EDI syntax, terminology and how a proper EDI file should look like,  this is not enough. Next is to study and read some sample edi message (best if the edi message is real message that generated from ERP system) and some existing mapping. Study and understand what are the edi message hierarchy level (header level vs item level) and how these segment map from original source.
Depend on the project or company you attached to, you will use different EDI software (or using SAP PI B2B-AddOn) to view message and do mapping.
One site free to see the hierarchy level of message is through stylusstudio.com website. Example:
http://www.stylusstudio.com/edifact/D97A/ORDERS.htm
In recent project, another consultant in my team shared this free tool, EDINotepad from  liaison.com. Try it out, it is a useful tool.
Now, you got both EDI syntax and message type, and know how to do edi mapping based on guide. This is the ‘Hard’ side of EDI only. To further extend the learning, you will need to understand the ‘Soft’ side of EDI. you need to understand more about the underlying business processes, understand the supply chain flow, goods flow and how the money flow, and match with the edi messages flow. Understand the purpose of each message type, and at least identify and understand some key mandatory fields in edi message.
Alright, that is my 2cent of first post about EDI. If you have any sharing tips, please leave your comment. Thanks.